Prime Minister Boris Johnson has been admitted to hospital for tests, 10 days after testing positive for coronavirus, Downing Street has said.
He was taken to a London hospital on Sunday evening with "persistent symptoms" - including a temperature.
It is said to be a "precautionary step" taken on the advice of his doctor.
The prime minister remains in charge of the government, but the foreign secretary is expected to chair a coronavirus meeting on Monday morning.
Mr Johnson is expected to stay overnight and is having what have been described as "routine tests", according to BBC Political Editor Laura Kuenssberg.
In a statement, 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."
She added: "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."
Mr Johnson has worked from home since it was announced that he had tested positive for coronavirus on 27 March.
He was last seen in public applauding the NHS and other key workers from his flat in Downing Street on Thursday evening, and chaired a coronavirus meeting remotely on Friday morning.
Also on Friday, the prime minister posted a Twitter video in which said he was still displaying minor symptoms.
"I still have a temperature. So in accordance with government advice I must continue my self isolation until that symptom itself goes," he said.
"But we're working clearly the whole time on our programme to beat the virus."
On Saturday, his pregnant partner Carrie Symonds tweeted that she has spent a week in bed with the main symptoms.
She said she had not been tested for the virus.
Health Secretary Matt Hancock had also tested positive for the virus and returned from self-isolation on Thursday to host the daily Downing Street news conference.
The government's chief medical adviser, Prof Chris Whitty, has also had to self-isolate after showing symptoms.
Last month, the prime minister's spokesman said if the prime minister was unwell and unable to work, Foreign Secretary Dominic Raab, as the first secretary of state, would stand in.
The news of Mr Johnson's admission to hospital came shortly after the Queen delivered a rallying message to the nation, saying the UK "will succeed" in its fight against the coronavirus pandemic.
