Boris Johnson has been admitted to hospital for tests as his coronavirus symptoms persist, Downing Street has said.
Number 10 said the Prime Minister was taken as a "precautionary step" on the advice of his doctor.
He tested positive for the virus 10 days ago, and has been in self-isolation inside his Downing Street flat since.
A Downing Street spokeswoman said: "On the advice of his doctor, the Prime Minister has tonight been admitted to hospital for tests.
"This is a precautionary step, as the Prime Minister continues to have persistent symptoms of coronavirus 10 days after testing positive for the virus.
Boris Johnson during the coronavirus outbreak
Boris Johnson during the coronavirus outbreak
In this handout photo provided by Number 10 Downing Street, Britain's Prime Minister Boris Johnson chairs the morning Covid-19 Meeting remotely after self isolating after testing positive for the coronavirus, at 10 Downing Street, London, Saturday, March 28, 2020. The new coronavirus causes mild or moderate symptoms for most people, but for some, especially older adults and people with existing health problems, it can cause more severe illness or death. (Andrew Parsons/10 Downing Street via AP)
ARCHIVO - En esta fotografía del jueves 2 de abril de 2020, el primer ministro británico Boris Johnson aplaude afuera de su casa en el número 11 de Downing Street para elogiar a los héroes locales que combaten el coronavirus, en Londres. (Pippa Fowles/10 Downing Street vía AP, archivo)
In this image taken from video of the TWITTER/@BorisJohnson, Britain's Prime Minister Boris Johnson speaks from self isolation which he has been in since contracting coronavirus, Friday April 3, 2020. British Prime Minister Boris Johnson has been admitted to a hospital with the coronavirus. Johnson’s office says he is being admitted for tests because he still has symptoms 10 days after testing positive for the virus. (TWITTER/@BorisJohnson via AP)
In this image taken from video of the TWITTER/@BorisJohnson, Britain's Prime Minister Boris Johnson announces he has tested positive for the new coronavirus, Friday March 27, 2020. Johnson's office said he was tested after showing mild symptoms and was now self-isolating, but would continue to lead the country's response to COVID-19. (TWITTER/@BorisJohnson via AP)
File photo dated 25/03/2020 of Health Secretary Matt Hancock watching Prime Minister Boris Johnson speak during Prime Minister's Questions in the House of Commons, London, both of them have tested positive for coronavirus.
File photo dated 23/03/2020 of a screen grab of Prime Minister Boris Johnson addressing the nation from 10 Downing Street, London. The Prime Minister has said he has tested positive for coronavirus.
File photo dated 20/03/2020 of Prime Minister Boris Johnson speaking at a media briefing in Downing Street, London, on coronavirus (COVID-19), he says he has tested positive for coronavirus.
File photo dated 20/03/2020 of Prime Minister Boris Johnson (centre), Chancellor Rishi Sunak (left) and Dr Jenny Harries (right) speaking at a media briefing in Downing Street, London, on coronavirus (COVID-19). The Prime Minister has said he has tested positive for coronavirus.
File photo dated 06/03/20 of Prime Minister Boris Johnson during a visit to the Mologic Laboratory in the Bedford technology Park in Bedfordshire, he says he has tested positive for coronavirus.
Prime Minister Boris Johnson outside 10 Downing Street, London, joining in with a national applause for the NHS to show appreciation for all NHS workers who are helping to fight the Coronavirus.
(EDITOR�S NOTE: Image Archived 25/03/2020)
Prime Minister Boris Johnson at one of his daily Downing Street Coronavirus Press Briefings.
Prime Minister Boris Johnson MP has tested positive for coronavirus, Downing Street has announced that Mr Johnson has mild symptoms and will self-isolate in Downing Street. He will still be in charge of the government's handling of the crisis, the statement added. (Photo by Keith Mayhew / SOPA Images/Sipa USA)
Prime Minister Boris Johnson leaves 10 Downing Street, London, for the House of Commons for Prime Minister's Questions.
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"The Prime Minister thanks NHS staff for all of their incredible hard work and urges the public to continue to follow the Government's advice to stay at home, protect the NHS and save lives."
A Number 10 spokesman insisted Mr Johnson remains "in charge of the Government" despite his hospital admission, and he has not handed responsibilities to his de facto deputy Dominic Raab.
However, Mr Raab is likely to chair the daily Covid-19 meeting on Monday morning for ministers and officials, which is usually led by the PM.
He is understood to be in an NHS hospital in London, where he will stay for "as long as needed".
Mr Johnson announced on March 27 that he had tested positive for Covid-19 and was self-isolating with "mild symptoms" including a high temperature and persistent cough.
He has shared several video updates from his Number 11 flat since his diagnosis, and stepped outside to join the nationwide clap for NHS staff on Thursday evening.
Mr Johnson has not been seen publicly since, but said he spoke to new Labour leader Sir Keir Starmer on Saturday afternoon.
Sir Keir wished the PM a "speedy recovery" after the announcement.