Boris Johnson has tested positive for the coronavirus.
The prime minister was tested after complaining of mild symptoms of the deadly disease. He is now self-isolating in Downing Street.
No.10 said he will remain in charge of the government's handling of the Covid-19 outbreak.
A Downing Street spokesperson said: “After experiencing mild symptoms yesterday, the prime minister was tested for coronavirus on the personal advice of England’s chief medical officer, Professor Chris Whitty.
“The test was carried out in No 10 by NHS staff and the result of the test was positive.
“In keeping with the guidance, the Prime Minister is self-isolating in Downing Street. He is continuing to lead the government’s response to coronavirus.”
The PM revealed the news in a video, saying: “Hi folks, I want to bring you up to speed with something that’s happening today - and that’s I’ve developed mild symptoms of the coronavirus.
“That’s to say a temperature and a persistent cough, and on the advice of the chief medical officer I’ve taken a test, that has come out positive so I am working from home, I’m 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 fight-back against coronavirus.”
Johnson added: “And I want to thank everybody who is involved, above all our amazing NHS staff, it was very moving last night to take part in that national clap for the NHS.
“But it’s not just the NHS, it’s our police, our social care workers, teachers, everybody who works in schools, DWP staff, an amazing national effort by the public services and by every member of the British public who is volunteering, an incredible response, 600,000 people have volunteered to take part in a great national effort to protect people from the consequences of coronavirus.
“I want to thank you, I want to thank everybody who is working to keep our country going through this epidemic, we will get through it, and the way we’re going to get through it is of course by applying the measures you will have heard so much about.
“The more effectively we all comply with those measures the faster our country will come through this epidemic, and the faster we will bounce back.
“So thank you to everybody who is doing what I’m doing, working from home, to stop the spread of coronavirus from household to household, that’s the way we’re going to beat it.
“We’re going to beat it, together. Stay at home, protect the NHS, and save lives.”