The prime minister remains in intensive care but is responding to treatment, Downing Street has said.
Boris Johnson remains in “good spirits” after spending his third night in hospital, his spokesman said.
The PM was admitted to St Thomas’ in London on Sunday night for tests after continuing to display symptoms of COVID-19, the disease caused by the coronavirus.
He was subsequently moved to intensive care on Monday night after his condition worsened.
Downing Street said Mr Johnson is no longer working while following the advice of doctors.
He is receiving just the “standard oxygen treatment” and is “breathing without any other assistance”, his spokesman said.
Foreign Secretary Dominic Raab, who has been asked to step in for the PM where necessary, once again chaired the government’s daily coronavirus meeting on Wednesday morning.
Asked if anyone has been in contact with Mr Johnson, the spokesman responded: “The PM is not working, he’s in intensive care, he has the ability to contact those that he needs to, he’s following the advice of his doctors at all times.”
He added that Number 10 was “hugely grateful” for the messages of support that have been sent to the PM since his hospital admission.
Britain is currently in the midst of a lockdown designed to halt the spread of COVID-19.
When he announced the measures last month, Mr Johnson said they would be reviewed every three weeks.
On Easter Monday, it will be three weeks since the lockdown was imposed.
But the PM’s admission to hospital – and subsequent move to intensive care – has thrown the timing of the review into question and raised fears of a power vacuum.
Downing Street said the three-week review of the lockdown will go ahead as planned, but that the public needed to “stick with it” at a “critical time” in the COVID-19 outbreak.
The PM’s spokesman said the review would take place “on or around” Easter Monday.
“Our focus for now needs to be relentlessly upon stopping the transmission of this disease while building capacity in the NHS. That is how we will save lives,” he said.
“We need to keep delivering a very clear message to the public that while this is difficult we need to stick with it.
“We are at a critical time in our fight against coronavirus and they need to stay at home, protect the NHS and save lives.”
:: Listen to the Daily podcast on Apple Podcasts, Google Podcasts, Spotify, Spreaker.
A health minister earlier told Sky News that it was “not the right moment” for the UK as a whole to consider relaxing the restrictions.
“We will be led by the scientific evidence of when is the right moment for the changes to be made,” Edward Agar told Kay Burley@Breakfast.
“At the moment that is not the right moment.”