Boris Johnson in hospital for Covid-19

British Prime Minister Boris Johnson has been admitted to hospital for tests in what Downing Street said was a "precautionary step" because he was showing persistent symptoms of coronavirus ten days after testing positive for the virus.

"On the advice of his doctor, the Prime Minister has tonight been admitted to hospital for tests," Downing Street said.

"This is a precautionary step, as the Prime Minister continues to have persistent symptoms of coronavirus ten days after testing positive for the virus," Downing Street said.

Johnson, 55, on March 27 became the first leader of a major power to announce that he had tested positive. He went into isolation at a flat in Downing Street and said on Friday he was staying there as he still had a high temperature.

Johnson continues to have a high temperature and Downing Street underscored that this was not an emergency admission. The prime minister's doctors considered it sensible for him to be seen in person.

Johnson remains in charge of the government, Downing Street said.

"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," Downing Street said.

Carrie Symonds, Johnson's 32-year-old pregnant fiancée, said on Saturday that she had spent the past week in bed with symptoms of the novel coronavirus but after seven days of rest felt stronger and was on the mend