China reported 508 new cases and another 71 deaths, 68 of them in the central city of Wuhan, where the epidemic was first detected in December. The updates bring mainland China's totals to 77,658 cases and 2,663 deaths.
South Korea now has the second-most cases in the world with 977 and has had a near 15-fold increase in reported infections in a week, as health workers continue to find batches in the southeastern city of Daegu and nearby areas, where panic has brought towns to an eerie standstill.
Of the 144 new cases reported by South Korea's Centers for Disease Control and Prevention, most came from Daegu and the surrounding areas of North Gyeongsang province.
The country also reported its 10th fatality from COVID-19, the name of the disease caused by the virus, including a man who had links to a hospital in Cheongdo, where a slew of infections has been reported among patients at a mental ward.
Korean Air, the country's biggest airline, said one of its cabin crew members tested positive for the virus, but it didn't immediately disclose details about the flights or routes the employee worked.
The government has vowed to full mobilized public health tools to contain the outbreak to the region surrounding Daegu, but says it isn't considering restricting travel. All Daegu citizens exhibiting cold-like symptoms, estimating around 30,000 people, will be tested for the virus. The country is also restricting exports to deal with nationwide shortages in masks.
Health authorities expected by Wednesday to finish testing some 1,300 members of the Daegu branch of the Shincheonji Church of Jesus who have exhibited symptoms, before expanding the tests.
The church, which has South Korea's biggest cluster of infections, has agreed to provide authorities a list of all of its 200,000 members nationwide so they could be screened, which could take months.
"It's a matter of speed and time — we must create a clear turning point within this week (to stem) the increase in confirmed cases," South Korean President Moon Jae-in said during a visit to Daegu City Hall. He promised "pan-national" support, including active employment of military, police and civilian resources, to combat the outbreak.
South Korea's cases now outnumber those reported by Japan, where the virus infected almost one-fifth of the passengers and crew on a cruise ship.
About 200 South Korean tourists on Tuesday returned home on a chartered flight arranged by Israel, which decided to send them back over virus concerns.
The U.S. Centers for Disease Control and Prevention on Monday advised Americans to "avoid all nonessential travel to South Korea" in its highest travel alert notice. Japan's Foreign Ministry urged citizens to avoid unessential trips to Daegu and North Gyeongsang province.
Clusters have also emerged in Iran and Italy, and there are concerns the new outbreaks could signal a serious new stage in the global spread of the illness.
Schools were closed in Iran for a second day, and daily sanitizing of public buses and the Tehran metro, which is used by some 3 million people, was begun.
In several countries that reported their first cases on Monday — Iraq, Afghanistan, Kuwait, Bahrain and Oman, the infected patients had links with Iran. Iraq and Afghanistan closed their borders with Iran in an effort to stop the further spread.
In Italy, where 229 people have tested positive for the virus and seven have died, police manned checkpoints around a dozen quarantined northern towns as worries grew across the continent.
Austria temporarily halted rail traffic across its border with Italy. Slovenia and Croatia, popular getaways for Italians, were holding crisis meetings. Schools were closed, theater performances were canceled and even Carnival celebrations in Venice were called off.
As outbreaks grew in more countries, the World Heath Organization said COVID-19 had the potential to be a pandemic but wasn't one yet.
"The past few weeks has demonstrated just how quickly a new virus can spread around the world and cause widespread fear and disruption," WHO's Director-General Tedros Adhanom Ghebreyesus said.
But "for the moment we're not witnessing the uncontained global spread of this virus," he said.
China still has the vast majority of the world's cases and deaths from COVID-19. On Monday, it postponed its most important political meetings of the year, indicating the importance President Xi Jinping places on fighting the epidemic that has posed one of his biggest political challenges.
The annual meetings of the National People's Congress and its chief advisory body usually held in March brings thousands of delegates to Beijing for discussions and political ceremony. State media noted many of those delegates are local leaders on the disease's front lines.
In South Korea, start of the new school year has been delayed and companies are telling employees to work from home. People who recently visited Daegu and nearby areas were advised to stay at home if possible for two weeks.
South Korea's professional basketball league said it will ban spectators until the outbreak is under control. Busan City said the world team table tennis championships it planned to host in March were postponed to June.
South Korea's military has confirmed 13 troops have the virus, resulting in quarantines for many other troops and halting field training. The United States Forces Korea says a 61-year-old widow of a retired soldier living in Daegu tested positive, the first infection among individuals related to U.S. troops in South Korea.
The allies are considering curtailing joint military exercises due to the outbreak.
Defense Secretary Mark Esper and South Korean Defense Minister Jeong Kyeong-doo told reporters in Washington the virus was a threat to their schedule of annual exercises.
Esper said he was confident they would find a way to protect troops while also ensuring both countries were ready to face potential threats.