Prime minister Boris Johnson has spent the duration of Monday night in an intensive care unit at St. Thomas’ Hospital in central London.
Johnson was moved following medical advice after his coronavirus symptoms became more severe.
A statement from Number Ten said that the prime minister was receiving “excellent care”.
The statement read: "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 [Monday] 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.
"The PM is receiving excellent care, and thanks all NHS staff for their hard work and dedication."
Johnson was originally admitted for tests after he had first announced that he had coronavirus 11 days ago, suffering from symptoms including a cough and a fever.
Foreign secretary and first secretary of state Dominic Raab will assume Johnson’s duties “where necessary”, but Johnson will continue to lead the government from hospital where possible.
Raab said at Monday’s daily coronavirus briefing that the prime minister would continue to “take the medical advice that he gets from his doctor” and act accordingly.
He said: "We have a team...that is full throttle making sure that his directions and his instructions are being implemented.”
Raab will once again chair the coronavirus briefing on Tuesday.
At this stage, it is not thought that the prime minister requires a ventilator and his moving to hospital was precautionary, despite needing to be administered with oxygen on Monday afternoon.
Chancellor of the Duchy of Lancaster Michael Gove informed the media on Tuesday morning that as of 09:00 BST, the prime minister was not using a ventilator and the country would be “updated” of any change in his condition.
The prime minister's pregnant partner Carrie Symonds confirmed on Saturday that she had spent a week resting in bed with the main symptoms of the virus but had not been tested.
The Queen is being kept up to date on the prime minister’s condition, while leaders elsewhere have issued messages of support.
New Labour leader Sir Keir Starmer described the update on the prime ministers condition as “terribly sad news", adding that the “country’s thoughts are with the prime minister and his family”.
US president Donald Trump said that Americans are “all praying"for the prime minister's safe recovery, describing him as "strong", a “very good friend” and “friend to our nation”.
The number of coronavirus deaths recorded in hospital in the UK has now reached 5,373, with 51,608 confirmed cases according to the Department of Health & Social Care.
