Boris Johnson had a "comfortable night" in St Thomas' Hospital, London, and is in "good spirits", the British Prime Minister's official spokesman has said.
Mr Johnson was taken to hospital last night as a "precautionary step" on the advice of his doctor.
He tested positive for the coronavirus 10 days ago, and had been in self-isolation inside his Downing Street apartment since.
Mr Johnson's official spokesman said he continued to lead the Government and had been working on official papers from his bed.
The British Prime Minister was said to be in "good spirits" after being taken to St Thomas' Hospital in London as a "precaution".
He remains under observation and the spokesman declined to give details of any treatment he had received or when he might be discharged.
"The Prime Minister was admitted to hospital for tests last night as a precaution. The issue is that his symptoms remain persistent," the spokesman said.
He added: "The Prime Minister had a comfortable night at St Thomas' Hospital in London and is in good spirits. He remains in hospital under observation."
In Mr Johnson's absence, the daily government coronavirus meeting was chaired by Dominic Raab, the British Foreign Secretary and First Secretary of State.
However, the PM's spokesman said that he had received his ministerial red box containing his official papers and was continuing to work from hospital.
"He continues to receive a box. The Prime Minister remains in charge of the Government."
In a video message posted to Twitter after his diagnosis was confirmed last week, Mr Johnson said: "I'm working from home and self-isolating and that's entirely the right thing to do.
"But, be in no doubt that I can continue thanks to the wizardry of modern technology to communicate with all my top team to lead the national fightback against coronavirus."