Boris Johnson is now self-isolating.
The Prime Minister, 55, was tested in Number 10 after experiencing mild symptoms yesterday (Thursday).
In a video on his Twitter account, Mr Johnson said he had developed a temperature and a persistent cough.
He added: "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.
"I want to thank everybody involved and, of course, our amazing NHS staff."
It is not known whether he is staying with his fiancee, Carrie Symonds, who is several months pregnant.
Earlier in the week it was announced that the Prince of Wales was also suffering "mild symptoms" of the disease.
The PM’s official spokesman said measures were being taken to ensure the illness does not spread further in government, but that No10 is a functioning workplace and staff can continue working following distancing guidelines until they begin showing symptoms.
The PM took part in the daily 9.30am coronavirus meeting of key government staff via video conferencing, and will continue to do so.
He will not take part in daily press conferences while self-isolating.
Foreign Secretary Dominic Raab is designated to stand in for the PM if needed, but Mr Johnson is currently continuing to carry out his role in full.
Last night he took part in the nationwide clap for NHS staff in Downing Street, along with Chancellor Rishi Sunak. The PM’s spokesman said: “He did really want to take part in clapping NHS staff, he felt it was important... he ensured he didn’t come into any close contact with anyone.”
On Thursday night Charles was seen for the first time since testing positive.
Clarence House posted a video in their Instagram Stories of heir to the throne Charles joining in with the round of applause for the NHS from Birkhall, his private home on the Balmoral estate in Scotland.
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.”