LONDON – British Prime Minister Boris Johnson was moved to an intensive care unit at a London hospital Monday night after his coronavirus symptoms worsened, his office said in a statement.

Johnson, 55, asked Foreign Secretary Dominic Raab "to deputize for him where necessary," according to a Downing Street statement.

"Since Sunday evening, the prime minister has been under the care of doctors at St. Thomas' Hospital, in London, after being admitted with persistent symptoms of coronavirus," the statement said.

Johnson tested positive for the respiratory illness March 27, the first major world leader to publicly acknowledge having COVID-19. His symptoms include a high temperature and a cough. He is conscious and has not been put on a ventilator.

President Donald Trump said Monday he asked four drug companies to contact Johnson's doctors to offer treatment to the prime minister, whom he called a "very good friend of mine and a friend to our nation."

"We'll see if we can be of help. We've contacted all of Boris' doctors and we'll see what is going to take place," Trump told reporters at a White House coronavirus task force briefing. "But when you get brought into intensive care that gets very serious with this particular disease."

It was unclear which companies the president was referring to, but he added they had met with prime minister's doctors about a "very complex treatment of things that they've just recently developed."

Earlier Monday, Johnson tweeted that he had a "comfortable night" and was in "good spirits" while receiving regular briefings from his Cabinet and government advisers.

Johnson's illness means that he has had to effectively step away from day-to-day governing as Britain, like much of the world, faces the worst public health crisis in a century. Britain has more than 52,000 confirmed cases and more than 5,300 deaths, and the virus could reach its peak in the country as soon as this weekend.

Britain's leader initially gambled that the country's best bet to overcome coronavirus would be to try to get to "herd" or majority immunity as quickly as possible. The thinking behind this was that it would protect the country in the long term if, as happened in the Spanish flu in 1918, a highly fatal second wave of infections occurred.

Johnson changed tactics in mid-March after researchers at Imperial College London projected that about 250,000 people in Britain would die if "chains of transmission" for the virus weren't immediately slowed or broken by a lockdown.

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Raab, 46, is Britain's first secretary of state and Johnson's de facto deputy. Though Britain does not have a written constitution indicating a clear line of succession, Johnson appointed him to run the country if he is incapacitated or unable to do it. Raab chaired the government's emergency coronavirus meeting Monday.

Like Johnson, Raab was a prominent member of the campaign for Britain to leave the European Union – Brexit. Though he will deputize for Johnson in his absence, it's not immediately clear whether he would automatically, permanently keep the role if Johnson were to die or whether there would need to be a vote to authenticate his premiership.

Britain elects a party, not an individual, meaning that Johnson's ruling Conservative Party would not necessarily be obliged to call an election.

Contributing: Courtney Subramanian