Prime Minister Boris Johnson has been moved to intensive care in hospital after his coronavirus symptoms “worsened”, Downing Street has said.
A spokesman said he was moved on the advice of his medical team and is receiving “excellent care”.
Mr Johnson has asked Foreign Secretary Dominic Raab to deputise “where necessary”, the spokesman added.
The prime minister, 55, was admitted to hospital in London with “persistent symptoms” on Sunday.
A No 10 statement read: “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.
“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.”
It continued: “The PM is receiving excellent care, and thanks all NHS staff for their hard work and dedication.”
Chancellor Rishi Sunak said his thoughts were with the prime minister and his pregnant partner, Carrie Symonds, and that Mr Johnson would “come out of this even stronger”.
Jeremy Corbyn Tweeted “My thoughts are with Boris Johnson and his family tonight. Thanks to the #NHS staff for their hard work and dedication. The new Labour leader Sir Keir Starmer described it as “terribly sad news”. saying “All the country’s thoughts are with the prime minister and his family during this incredibly difficult time,” he added.
My thoughts are with Boris Johnson and his family tonight.— Jeremy Corbyn (@jeremycorbyn) April 6, 2020
Thanks to the #NHS staff for their hard work and dedication.
Mr Johnson was initially taken to hospital for routine tests after testing positive for coronavirus 10 days ago. His symptoms included a high temperature and a cough.
Earlier on Monday, he tweeted that he was in “good spirits”.
Last night, on the advice of my doctor, I went into hospital for some routine tests as I’m still experiencing coronavirus symptoms. I’m in good spirits and keeping in touch with my team, as we work together to fight this virus and keep everyone safe.— Boris Johnson #StayHomeSaveLives (@BorisJohnson) April 6, 2020
It comes as the number of coronavirus hospital deaths in the UK reached 5,373 – an increase of 439 in a day.
The Department of Health and Social Care said there were now 51,608 confirmed coronavirus cases in the U.K.