The 55-year-old U.K. leader spent three nights in the intensive care unit at St. Thomas' Hospital in London after his COVID-19 symptoms worsened. He was moved back to a regular ward on Thursday evening, and his office said he was in "the early phase of his recovery."

His father said the prime minister needs to "rest up."

"He has to take time," Stanley Johnson told the BBC. "I cannot believe you can walk away from this and get straight back to Downing Street and pick up the reins without a period of readjustment."

Johnson was diagnosed with COVID-19 two weeks ago, the first world leader confirmed to have the illness, and initially was said to have mild symptoms including fever and a cough. He was admitted to the hospital on Sunday and moved the next day to the ICU, where he received oxygen but was not put on a ventilator.

Acknowledging the seriousness of the prime minister's condition, Stanley Johnson said his son "almost took one for the team."

Intensive care specialist Duncan Young said it is "almost impossible to know" how long it will take Johnson to get back to full health.

"He has been very ill and it will take a while," Young said. "Nobody knows in terms of shortness of breath and lethargy, in scientific literature, how long it takes to recover. It particularly depends on how ill you have been."

Foreign Secretary Dominic Raab is standing in for Johnson while he is ill

As Johnson recovered in the hospital, his government implored people not to travel to see relatives or visit second homes over the Easter holiday weekend as Britain's death toll from COVID-19 continues to rise.

Almost 8,000 people with the coronavirus have died in British hospitals, according to government figures. While the number of new confirmed cases has begun to plateau, deaths have neared the peaks seen in Italy and Spain, the two countries with the greatest number of fatalities.

On Thursday, the U.K. reported 881 new deaths. Italy recorded a high of 969 deaths on March 27 and Spain 950 deaths on April 2.

For most people, the coronavirus causes mild to moderate symptoms such as fever and cough. But for some, especially older adults and the infirm, it can cause pneumonia and in some cases death.

U,K. authorities say restrictions on business and public activity imposed March 23 to try to slow the spread of the virus are likely to last at least several more weeks.

"It's still too early to really be confident that we are turning the corner," said Stephen Powis, medical director of the National Health Service in England.

Some British officials have been accused of flouting their own rules, which bar most travel outside the home except for essential shopping and exercise.

Scotland's chief medical officer, Catherine Calderwood, was forced to resign earlier this week after twice traveling to her second home.

And Housing Secretary Robert Jenrick was criticized for traveling from London to his house in central England, then making another 40-mile (60-kilometer) journey to visit his parents.

Opposition Labour Party lawmaker Nick Thomas-Symonds said "it's very important for public confidence that Robert Jenrick explains himself and why exactly that journey was necessary."

Jenrick said he went to his parents' house to deliver "essentials —including medicines" to his parents, who are self-isolating. Delivering medicines to vulnerable people is permitted under the U.K. lockdown rules.