Senate Majority Leader Mitch McConnell abruptly eased his restrictive proposed rules for President Donald Trump's impeachment trial , backing off the condensed two-day schedule to add a third for opening arguments after protests from senators, including Republicans.

The trial quickly burst into a partisan fight at the Capitol as the president's lawyers opened arguments Tuesday in support of McConnell's plan. Democrats objected loudly to McConnell's initially proposed rules, and some Republicans made their concerns known in private at a GOP lunch.

Without comment, the Republican leader quietly submitted an amended proposal after meeting behind closed doors with his senators as the trial opened. The handwritten changes would a dd the extra day and allow House evidence to be included in the record. There is still deep disagreement about calling additional witnesses.

"It's time to start with this trial," said White House Counsel Pat Cipollone, the president's lead lawyer in brief remarks  as the proceedings opened in public.

"It's a fair process," he said. "There is absolutely no case."

Chief Justice John Roberts gaveled open the session, senators having taken an oath last week to do "impartial justice" as jurors. House House prosecutors were on one side, Trump's team on the other, in the well of the Senatem as senators sat silent at their desks.

Senators were stunned by McConnell's shift, and aides offered no immediate answers.

But a spokeswoman for Republican Sen. Susan Collins said that she and others had raised concerns. The Maine senator sees the changes as significant improvements, said spokeswoman Annie Clark.

The turnaround was a swift lesson as the White House's wishes run into the reality of the Senate. The White House wanted a session crammed into a shorter period to both expedite the trial and shift more of the proceedings into late night, according to a person familiar with the matter but unauthorized to discuss it in public.

"READ THE TRANSCRIPTS!" the president tweeted from miles away, as he returned to his hotel at a global leaders conference in Davos, Switzerland. That's the transcript of his phone call in which he asked new Ukrainian President Volodymyr Zelenskiya for "a favor." The Democrats cite that transcript as solid evidence against Trump, though he repeatedly describes it as "perfect."

Democrats had warned that the rules package from Trump's ally, the Senate GOP leader, could force midnight sessions that would keep most Americans in the dark and create a sham proceeding.

"This is not a process for a fair trial, this is the process for a rigged trial" Rep. Adam Schiff, D-Ca., the chairman of the House Intelligence Committee leading the prosecution, told reporters. He called it a "cover-up."

Schiff opened his arguments before the Senate playing a video of Trump calling for more witnesses to testify. Schiff noted the sudden change in proposed rules, made moments before he spoke.

"The facts will come out in the end," Schiff said. "The question is, will it come out in time? "

McConnell said, "The president's lawyers will finally receive a level playing field," contrasting it with the House impeachment inquiry.

The rare impeachment trial, unfolding in an election year, is testing whether Trump's actions toward Ukraine warrant removal at the same time that voters are forming their own verdict on his White House.

Just weeks before the first Democratic primary contests, four senators who are also presidential candidates were off the campaign trail, seated as jurors.

"My focus is going to be on impeachment," Sen. Bernie Sanders, the Vermont independent running for the Democratic nomination, told reporters. He said his supporters would keep working "to defeat the most dangerous president in American history."

The Democrats say the prospect of middle-of-the-night proceedings, without allowing new witnesses or even the voluminous House records of the trial, would leave the public without crucial information about Trump's political pressure campaign on Ukraine and the White House's obstruction of the House impeachment probe.

Rep. Jerry Nadler, the Judiciary Committee Chairman also leading the House team, said: "There's no trial in this country where you wouldn't admit relative witnesses."

Trump's legal team doesn't dispute Trump's actions — that he called the Ukraine president and asked for a "favor" during a July 25 phone call. In fact, the lawyers included the rough transcript of Trump's conversation as part of its 110-page trial brief submitted ahead of the proceedings.

Instead the lawyers for the president, led Cipollone and a TV-famous legal team including Alan Dershowitz, say the two charges against the president don't amount to impeachable offenses and Trump committed no crime.

Legal scholars have long insisted the framers of the Constitution provided impeachment as a remedy for "other high crimes and misdemeanors," a particularly broad definition that doesn't mean simply specific criminal acts.

Democrats in prosecuting the case against the president point in particular to a General Accountability Office report that found the White House violated federal law by stalling money to Ukraine that had been approved by Congress.

House Democrats, responding Tuesday to arguments by Trump's legal team, said the president's legal filing confirmed that "his misconduct is indefensible."

They wrote, "President Trump's lengthy brief to the Senate is heavy on rhetoric and procedural grievances, but entirely lacks a legitimate defense of his misconduct." The president would "rather discuss anything other than what he actually did," the Democrats wrote.

Roberts administered the oath to one remaining senator, James Inhofe, who was attending a family medical issue in Oklahoma last week when the other senators vowed the oath and signed the oath book.

Also Tuesday, the House Democratic managers overseeing the impeachment case asked Cipollone, the president's lead lawyer at the trial, to disclose any "first-hand knowledge" he has of the charges against Trump. They said evidence gathered so far indicates that Cipollone is a "material witness" to the allegations at hand.

House Democrats impeached the Republican president last month on two charges: abuse of power by withholding U.S. military aid to Ukraine as he pressed the country to investigate Democratic rival Joe Biden, and obstruction of Congress by refusing to cooperate with their investigation.

No president has ever been removed from office by the Senate. With its 53-47 Republican majority, the Senate is not expected to mount the two-thirds voted needed for conviction. Even if it did, the White House team argues it would be an "'unconstitutional conviction'' because the articles of impeachment were too broad.

The impeachment trial against U.S. President Donald Trump kicked off Tuesday in the Senate as the chamber debated, and would later vote on, a resolution stipulating rules guiding the process.

Face masks sold out and officials at airports and train stations checked passengers for fevers as China on Tuesday sought to control the outbreak of a new virus that has reached four other countries and territories and threatens to spread further during the Lunar New Year travel rush.

Anxiety grew both at home and abroad after Chinese government expert Zhong Nanshan confirmed fears on state television late Monday that the new type of coronavirus can spread from human to human.

Six people have died and 291 have been infected in China, the National Health Commission said Tuesday.

The stock prices of some companies that sell masks rose Tuesday, but markets fell in much of Asia as investors worried about the potential impact on tourism and the economy.

Concerned about a global outbreak similar to SARS, another coronavirus that spread from China to more than a dozen countries in 2002-2003, numerous nations have adopted screening measures for travelers from China, especially those arriving from Wuhan, the central city where the virus appears to have originated.

An airport staff member uses a temperature gun to check people leaving Wuhan Tianhe International Airport in Wuhan, China, Tuesday, Jan. 21, 2020. Photo: AP

Guards at Wuhan's airport pointed electronic thermometers at travelers. Several online retailers were sold out of masks, which were being sold for more than 10 times their original price. Users of the popular Weibo social media platform urged others to wash their hands and stay home.

Outside the Wuhan Medical Treatment Center, where many of the coronavirus patients are receiving care, several workers were dressed in full-body biohazard suits, supplemented by goggles, masks and plastic wrapped around their shoes.

While many wore masks in Wuhan, streets were far from deserted and people appeared to be carrying on with their regular activities.

"I'm not that worried," said Helen Cao, a Wuhan resident who was shopping on a downtown avenue lined with stores and full of pedestrians. Like many in the city, she began wearing a mask after hearing Zhong's assessment of human-to-human transmission.

"Maybe people from other places are more concerned about our health, but (Wuhan) locals actually are continuing to eat, go out and take strolls, go clubbing at night," Cao said. "Everything's very normal, everyone's just wearing masks, nothing more."

Initial symptoms of the new coronavirus include fever, cough, tightness of the chest and shortness of breath.

The first cases late last month were connected to a seafood market, and transmission was thought to be occurring from animals to humans. Authorities previously had not confirmed human-to-human transmission.

People wear face masks as they ride an escalator at the Hong Kong International Airport in Hong Kong, Tuesday, Jan. 21, 2020. Photo: AP

In addition to 258 cases in Wuhan, more than 20 have been diagnosed in Beijing, Shanghai, Guangdong province in the south and Zhejiang in the east. Four cases have been confirmed overseas among Chinese travelers in South Korea, Japan and Thailand. A Taiwanese businesswoman who just returned from Wuhan tested positive for the virus, Taiwan's Centers for Disease Control reported Tuesday.

Fifteen medical workers have also tested positive for the virus, the Wuhan Municipal Health Commission said.

Two cases in Guangdong were people who had not visited Wuhan but fell ill after family members returned from there. Zhong cited those as evidence the disease had spread between humans.

Australia, Japan, South Korea and the U.S. were among the countries increasing airport screenings. Three weekly direct flights from Wuhan to Sydney will be met by border security and biosecurity staff for assessments, chief Australian medical officer Brendan Murphy told reporters.

"Please take every possible precaution," Japanese Prime Minister Shinzo Abe instructed the health minister and other government departments.

The coronavirus family includes those that cause the common cold, but some found in bats, camels and other animals have evolved into more severe illnesses like SARS, or severe acute respiratory syndrome, and MERS, Middle East respiratory syndrome.

The possibility the virus can be transmitted between people increases the chances it could spread faster and more widely. The Chinese government has estimated people will make around 3 billion trips during the Lunar New Year travel season, but some social media users have said they may stay home due to concern about the virus.

In his first public remarks on the illness, Chinese President Xi Jinping instructed government departments to promptly release information on the virus and deepen international cooperation.

Police stand guard outside Wuhan Huanan Wholesale Seafood Market, where a number of people related to the market fell ill with a virus in Wuhan, China, Tuesday, Jan. 21, 2020. Photo: AP

When SARS began infecting people in southern China, the Chinese government initially tried to conceal the severity of the epidemic, which ended up killing nearly 800 people. The cover-up was exposed by a high-ranking physician.

Gabriel Leung, dean of medicine at the University of Hong Kong, said Chinese authorities have responded much more quickly this time.

"Our underlying assumptions are the force of infection is very different now ... because so many public health measures have been undertaken and so many interventions have been executed," Leung told reporters at a briefing.

Leung, who was heavily involved in the response to SARS, said modeling shows that cases will multiply over the coming weeks but the outbreak will gradually lose momentum as precautions take effect.

For the moment, the new coronavirus appears to be far less lethal than SARS.

"Based on current information, an animal source seems the most likely primary source of this outbreak with limited human-to-human transmission occurring between close contacts," World Health Organization spokesman Tarik Jasarevic said at a briefing.

"Based on current data, some new cases seem to experience milder diseases which is within the milder end of the spectrum of symptoms caused by respiratory illnesses," Jasarevic said.

Chinese foreign ministry spokesman Geng Shuang pledged rigorous measures to tackle the virus.

"We will resolutely contain the spread of the epidemic," Geng said.

Surgical masks were mandatory Tuesday at Beijing United Family Hospital, where all visitors had their temperatures taken at the entrance.

At one pharmacy in Shanghai, a shopkeeper named Liu Zhuzhen said more than 100 people had bought masks by midday. They were already sold out despite having recently been restocked.

3M, an American brand popular in China for anti-pollution masks, was sold out of masks on its official online stores on e-commerce platforms Taobao and JD.com as of Tuesday afternoon. Other retailers were selling 3M masks at a markup, including for as much as 40 yuan ($7) a mask. Websites that track online pricing show the same masks used to sell for 3 yuan (53 cents) each.

State broadcaster CCTV quoted Wuhan Mayor Zhou Xianwang urging limitations on travel.

"Unless it's necessary, people outside should not come to Wuhan, and citizens of Wuhan should not leave the city," Zhou said.

A U.S. resident who recently returned from a trip to central China has been diagnosed with the new virus that has sparked an outbreak and stringent monitoring around the world, U.S. health officials said Tuesday.

The man returned to the Seattle area in the middle of last week after traveling to the Wuhan area, where the outbreak began. The man is in his 30s and is in good condition at a hospital in Everett, outside Seattle. He's not considered a threat to medical staff or the public, health officials said.

Officials said he had no symptoms when he arrived at the Seattle-Tacoma airport, but he contacted doctors on Sunday when he started feeling ill.

The U.S. is the fifth country to report seeing the illness, following China, Thailand, Japan, and South Korea.

Late last week, U.S. health officials began screening passengers from central China at U.S. airports. Officials around the world have implemented similar airport screenings in hopes of containing the virus during the busy Lunar New Year travel season.

Last month, doctors began seeing a new type of viral pneumonia — fever, cough, difficulty breathing — in people who spent time at a food market in Wuhan. More than 275 cases of the newly identified coronavirus have been confirmed in China, most of them in Wuhan, according to the World Health Organization.

The count includes six deaths — all in China, most of them age 60 or older, including at least some who had a previous medical condition.

Officials have said it probably spread from animals to people, but this week Chinese officials said they've concluded it also can spread from person to person.

In announcing the airport screenings last week, CDC officials said then risk to the American public was low but that it was likely the illness would appear in the U.S. at some point.

The UN Food and Agriculture Organization (FAO) on Tuesday said South Sudan is at a high risk of invasion by desert locust amid worsening food security situation in the country.

Meshacko Malo, FAO country representative, said assistance is urgently required to avert locust invasion and minimize their devastating impacts on food security.

"The immediate threat of South Sudan are from the two major points, one on the Kapoeta east area once given the wind that could migrate from the Kenyan direction and from the Ethiopian side that could migrate and attack the region of Renk area which is an important food basket of the country," Malo said in Juba.

He said that the governments of Kenya and Ethiopia have tried to control the pests, though some were spotted 200 kilometers away from South Sudan's Kapoeta region that is near the Kenyan border.

"Once we are in a fly situation then it is easy to move to the threat situation although we are still working with the colleagues in Kenya, particularly with government authorities and desert locust control organization that has planes that could respond to this fight," said Malo.

Onyoti Adigo, South Sudan's agriculture and food security minister, said the government has formed a high-level committee to support the coordination control measures, saying that the community awareness will soon commence where experts further train field level experts to facilitate the monitoring and control mechanism.

"These proactive steps and preparatory efforts ahead of the threat are crucial in the fight against desert locust," Adigo said.