British Prime Minister Boris Johnson was spending a second night in intensive care battling the coronavirus which has infected more than 55,000 across the country and killed nearly 6,200.

"He stayed at work for you... now pray at home for him," The Sun tabloid splashed across its front page Wednesday while the Daily Express said: "Boris 'will pull through'."

British Prime Minister Boris Johnson
British Prime Minister Boris Johnson was moved to intensive care on Monday. Photo: AFP / STAFF

Deputising for Johnson, Foreign Secretary Dominic Raab said he was "confident he'll pull through, because if there's one thing I know about this prime minister, he's a fighter and he'll be back, leading us through this crisis in short order".

In an update Tuesday evening, the prime minister's spokesman said his "condition is stable and he remains in intensive care for close monitoring."

He earlier said the 55-year-old Conservative leader was receiving "standard oxygen treatment and breathing without any other assistance" and had not required a ventilator.

British foreign secretary Dominic Raab
Foreign Secretary Dominic Raab is Johnson's de facto deputy. Photo: 10 Downing Street / Pippa FOWLES

Johnson is the most high-profile government leader to become infected with COVID-19 and messages of support flooded in from across Britain and the world.

He was admitted to intensive care on Monday evening after spending Sunday night in hospital following concerns he still had a cough and high temperature 10 days after being diagnosed with COVID-19.

British Prime Minister Boris Johnson
British Prime Minister Boris Johnson spent the night in the ICU with a deteriorating case of coronavirus. Photo: AFPTV / William EDWARDS

His transfer to intensive care is unprecedented for a prime minister during a national emergency.

For many people, it brought home the seriousness of the disease that has so far seen 6,159 deaths in Britain, with a record 786 more reported in a daily update on Tuesday.

British Prime Minister Boris Johnson
Before being hospitalised Boris Johnson took part in a national "clap for carers" to show thanks for the health workers battling the coronavirus pandemic. Photo: 10 Downing Street / Pippa FOWLES

Despite the record daily death toll, there was more encouraging news with the number of new daily cases remaining at a roughly stable 3,643.

In a round of broadcast interviews, senior minister Michael Gove insisted the "work of government goes on".

British foreign secretary Dominic Raab
Britain's Foreign Secretary Dominic Raab is Johnson's de facto deputy. Photo: AFP / Tolga AKMEN

He later said he was now staying at home after a family member displayed mild coronavirus symptoms.

Raab chaired the daily coronavirus meeting in the prime minister's place on Tuesday.

Boris Johnson is at St Thomas' Hospital
The media has flocked to St Thomas' Hospital. Photo: AFP / Isabel Infantes

"There is a clear plan... the government and the cabinet are working together to implement that plan," Johnson's spokesman said when asked if there was a power vacuum in Britain.

The country does not have a formal constitutional role of deputy prime minister, and experts said Raab would need the support of the rest of the cabinet to make any big decisions.

The most pressing issue is a review expected next week on whether to continue the nationwide lockdown introduced on March 23 to try to stem the spread of COVID-19.

Boris Johnson and Carrie Symonds
Johnson with his partner Carrie Symonds, who is pregnant with their first child together. Photo: POOL / Stefan Rousseau

Johnson announced on March 27 that he had coronavirus and went into self-isolation in a flat above his Downing Street office.

But on Monday evening he was moved to intensive care in London's St Thomas' hospital after his condition worsened.

The prime minister has received messages of support from around the world, with US President Donald Trump sending best wishes to his "very good friend" while Russian leader Vladimir Putin said Johnson's "energy, optimism and sense of humour" would see him through.

For some, Johnson's larger-than-life personality has made his hospitalisation all the more shocking.

His biographer Andrew Gimson said Johnson always made him feel upbeat, and "now here he is the stricken one".

"This is an enormous shock, completely unfamiliar territory for all those who know him," he told BBC radio.

Experts said it was not uncommon for coronavirus patients to move to intensive care, but said it showed Johnson's condition was serious.

"There is no doubt this turn of events means Boris Johnson is extremely sick," said Derek Hill, professor of medical imaging at University College London.

The British government was criticised for initially refusing to follow other European countries in requiring people to stay home as the virus spread rapidly across the globe.

Johnson himself said in early March that he was still shaking hands with people.

Two weeks ago, he ordered a nationwide lockdown, but parliament continued to sit for several days after and Westminster became a hotspot for the virus.

Health Secretary Matt Hancock and the heir to the throne, Prince Charles, have both been infected, although they have since recovered.

Johnson's pregnant partner, Carrie Symonds, moved out of Downing Street after some staff fell ill.

But she said on Saturday she had just spent a week in bed with symptoms, although she has not been tested.

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