Britain's Queen Elizabeth II records her address to the UK and the Commonwealth in relation to the coronavirus outbreak at Windsor Castle, west of London on Sunday. Photo: AFP

Prime Minister Boris Johnson continues to lead the government, Housing Minister Robert Jenrick said Monday after the British leader spent the night in hospital for tests because he was still suffering symptoms of the coronavirus.

"He's been working extremely hard, leading the government and being constantly updated, that's going to continue," Jenrick told BBC TV.

"Obviously today, he's in hospital having the test but he'll continue to be kept informed as to what's happening and to be in charge of the government." 

Johnson was taken to hospital after failing to shake off coronavirus symptoms, as Queen Elizabeth II said a united effort would defeat the outbreak.

The government announced within an hour of the monarch's rare special address Sunday to the country and Commonwealth nations that Johnson had been admitted for further tests as a precaution.

Johnson, 55, had been due to reemerge from seven days of self-isolation on Friday, a week after announcing he had tested positive for COVID-19 and had mild symptoms. But he said in a video message on Friday that he would continue to stay at home because of a persistent high temperature.

Downing Street called it a "precautionary step" and it is understood his admission was not an emergency and he was taken to hospital on medical advice.

Foreign Secretary Dominic Raab is designated to take over if the prime minister is unable to perform his duties.

Johnson is the most high-profile world leader to contract the virus. His pregnant partner, Carrie Symonds, is also recovering from symptoms but has not been tested.

Medical experts said doctors would likely be assessing Johnson's lung and heart function.

"Doctors will be monitoring important vital signs such as oxygen saturations," said Rupert Beale, a group leader at the cell biology of infection laboratory at the Francis Crick Institute.

"They will also check blood tests to see what the immune response to the virus looks like, and to assess liver and kidney function."

The Downing Street announcement came as the 93-year-old queen offered a message of hope to everyone affected by the global pandemic.

The monarch's eldest son Prince Charles, heir to the throne, has tested positive after displaying mild symptoms.

In only her fourth address at a time of crisis in her 68-year reign, the queen said the outbreak could be defeated by a collective effort in a "common endeavor."

"We will succeed - and that success will belong to every one of us," she said in a speech recorded at Windsor Castle, west of London, where she moved as a precaution on March 19.

Thanking health care staff and key workers, and praising the community response to the outbreak, the queen said people in Britain and around the world could feel proud.

"Together we are tackling this disease, and I want to reassure you that if we remain united and resolute, then we will overcome it," she added.

She drew on her experience of World War II, when she and her sister princess Margaret were evacuated to Windsor as London was bombed, drawing parallels with people forced apart by the virus.

In particular, she referenced British wartime singer Vera Lynn, whose song "We'll Meet Again" became an anthem for service personnel fighting abroad, far from their loved ones.

"We should take comfort that while we may have more still to endure, better days will return: We will be with our friends again; we will be with our families again; we will meet again."