A spokesperson for No.10 said: “On the advice of his doctor, the prime minister has tonight been admitted to hospital for tests.
“This is a precautionary step, as the prime minister continues to have persistent symptoms of coronavirus 10 days after testing positive for the virus.
“The prime minister thanks NHS staff for all of their incredible hard work and urges the public to continue to follow the government’s advice to stay at home, protect the NHS and save lives.”
Johnson is understood to be in an NHS hospital in London where he will stay for “as long as needed”.
Foreign secretary Dominic Raab is likely to chair the daily Covid-19 meeting on Monday morning for ministers and officials, which is usually led by the PM.
Conservative MP Andrea Leadsom tweeted: “Praying for a speedy recovery for our Prime Minister.”
Labour MP Jess Phillips sent her regards to Johnson and his pregnant fiancee Carrie Symonds.
“Sending regards to the Prime Minister and his family and friends especially to Carrie, it must be such a worry,” the former leadership candidate tweeted
It comes as Symonds, 32, revealed on Saturday that she has been suffering from coronavirus symptoms.