"On the advice of his doctor, the Prime Minister has tonight been admitted to hospital for tests", a Downing Street spokesperson said.
Within an hour of the Johnson announcement, Scotland's chief medical officer Catherine Calderwood resigned after she was photographed by The Scottish Sun visiting her holiday home on the east coast of the country over the weekend.
Johnson, 55, felt unwell on March 26 and took a test for the virus, which confirmed he had the illness.
The following day he announced he was in isolation, and has been unable to shake off the symptoms - including a high temperature - since.
Another UK government official who has been affected by the disease include Health Minister Nadine Dorries who tested positive for COVID-19.
Newsweek reached out to Downing Street for additional information.
Johnson's partner Carrie Symonds, who is pregnant with their child, also reportedly caught the virus, but is improving.
Health Secretary Matt Hancock returned to work on Friday after a week at home following his positive test for COVID-19.
In a message on Friday he said he was feeling better but still had a fever.
On March 27, he became the first leader of a major power to announce he had tested positive for COVID-19.
"While we have faced challenges before, this one is different", said the Queen, in what was only her fifth such address over her 68-year reign. We will succeed - and that success will belong to every one of us.
In particular, she referenced British wartime singer Vera Lynn, whose song "We'll Meet Again" became an anthem for service personnel fighting overseas, far from their loved ones.
There were fears warm spring weather on Sunday would encourage Britons to head to parks. But on Sunday night Calderwood said she had quit as her behavior risked "becoming a distraction".
Catherine Calderwood caused outrage in Scotland for twice visiting her second home north of Edinburgh, despite fronting an ad campaign calling for Scots to stay at home.