UK Prime Minister Boris Johnson has tested positive for coronavirus and is self-isolating in Downing Street.
Mr Johnson is thought to be the first world leader to announce that he has the virus.
Johnson received the result at midnight, just hours after he was seen clapping outside No 10 as part of a nationwide gesture to recognise and thank NHS staff and carers for going above and beyond during this epidemic.
In a video on his Twitter account,he 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 fight-back against coronavirus."
He said he had experienced mild symptoms over the past 24 hours, including a temperature and cough, but would continue to lead the government.
Earlier this week the prime minister's spokesman said if Mr Johnson was unwell and unable to work, Foreign Secretary Dominic Raab, as the first secretary of state, would stand in.
Figures rising by the day
Another 181 people died with the virus in the past day, figures showed.It takes the total number of UK deaths to 759, with 14,543 confirmed cases.
The daily coronavirus news conference was led by Cabinet Office minister Michael Gove, alongside deputy chief medical officer Dr Jenny Harries and NHS England chief executive Sir Simon Stevens.
The government has imposed strict restrictions on everyday life designed to slow the spread of the virus.
The UK's chief scientific adviser Sir Patrick Vallance has said he expects the number of coronavirus cases to increase over the next two to three weeks, and then start to gradually decrease due to the current lockdown.
The number of people who have volunteered to help the NHS has reached 700,000. The government originally set a target of 250,000 but increased it to 750,000 after a huge response.
More than 7,000 former nurses and midwives have signed up to return to support.
Meanwhile, Health Secretary Matt Hancock has tested positive for the virus while England's Chief Medical Officer, Prof Chris Whitty, has shown symptoms and is self-isolating.
Mr Hancock, who is responsible for the NHS, said he would self-isolate until next Thursday.
Professor Whitty, who has not taken a test, said he would continue to advise the government on the medical response to coronavirus, supported by his deputies.
The PM and the health secretary have had repeated contact with senior political figures, including cabinet members, and advisers in the last few days. However, no other ministers or advisers will be tested for the virus unless they show symptoms, Downing Street said.
No 11 and the four-bedroom flat, which was previously occupied by the former prime ministers David Cameron and Tony Blair, have been sealed off from No 10 and No 12 by shutting the doors that staff and government officials use to move between the buildings.
The prime minister will work from the office usually used by the chancellor, who has given it over to Johnson during his period of isolation. It is kitted out with full videoconferencing equipment.