Boris Johnson has been moved to intensive care after his condition worsened on Monday, Downing Street has announced.
The prime minister, who has COVID-19, was moved to the intensive care unit at St Thomas' hospital at around 7pm on Monday night. He remains conscious at this time and has been moved as a precaution should he require ventilation to aid his recovery, his office said.
"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," a Number 10 spokesperson said.
"Over the course of this afternoon, the condition of the prime minister has worsened and, on the advice of his medical team, he has been moved to the Intensive Care Unit at the hospital."
Dominic Raab, the foreign secretary, will deputise for the prime minister in leading the UK's response to the coronavirus.
Confirming to reporters that he would be standing in for Johnson, Raab said: "We'd like to take this opportunity as a government to thank NHS staff up and down the country for all of their dedication, hard work and commitment in treating everyone who's been affected by this awful virus."
Asked if the public should be worried about the prime minister's health, Raab replied: "The government's business will continue, and the prime minister is in safe hands with a brilliant team at St Thomas' hospital, and the focus of the government will be making sure the prime minister's direction — all the plans that mean we can defeat coronavirus and pull the country through this challenge — will be taken forward.
"There's an incredibly strong team spirit behind the prime minister and making sure that we get all of the plans that the prime minister has instructed us to deliver — to get them implemented as soon as possible.
"The PM is receiving excellent care, and thanks all NHS staff for their hard work and dedication," he added.
The chancellor, Rishi Sunak, tweeted that he would "come out of this even stronger" and offered his thoughts to Johnson's pregnant partner, Carrie Symonds.
The new Labour leader, Keir Starmer, also tweeted his support to Johnson and his family.
Johnson's predecessor as prime minister, Theresa May, offered her thoughts and prayers.
Buckingham Palace said the Queen, who remains at Windsor Castle, would be "kept informed" by Downing Street on Johnson's condition.
In a statement, the speaker of the House of Commons, Lindsay Hoyle, said: "This is terrible news. I know the thoughts and prayers of everyone across the House are with the Prime Minister and his family right now. We all wish him a speedy recovery."
Johnson was thought to be the first world leader to announce they had the virus. In a video posted on March 27, he said: "I'm working from home and self-isolating and that's entirely the right thing to do."
Last week, despite concerns, he continued to lead cabinet meetings from his study via video link and appeared outside his door in Downing Street on Thursday to join a nationwide applause of National Health Service workers.
In a tweet sent earlier on Monday, he said: “I’m in good spirits and keeping in touch with my team, as we work together to fight this virus and keep everyone safe."