Boris Johnson has spent a second night in intensive care as he continues to receive treatment for coronavirus.
Mr Johnson is being kept in St Thomas’ Hospital in London “for close monitoring”, Downing Street said.
The PM is “comfortable, he’s stable, he’s in good spirits”, said health minister Edward Argar on Wednesday.
No 10 also suggested the three-week review into whether the coronavirus lockdown could be eased would not go ahead as planned on Monday.
Asked on BBC Breakfast when the measures might be lifted, Mr Argar said the scientific evidence “isn’t yet there to allow us to make us a decision”.
“We have to be over that peak before we can think about making changes,” he said, adding: “It’s too early to say when we will reach that peak.”
Foreign Secretary Dominic Raab, who is deputising for the PM, said on Tuesday he was “confident” the PM would recover from this illness, describing him as a “fighter”.
Speaking at the Downing Street coronavirus briefing, he said Mr Johnson was receiving standard oxygen treatment and was breathing without any assistance, such as mechanical ventilation or non-invasive respiratory support.
The prime minister was admitted to St Thomas’ on Sunday, on the advice of his doctor, after continuing to display symptoms of a cough and high temperature 10 days after testing positive for the virus.
Mr Raab said the prime minister was being monitored closely in critical care, as was usual clinical practice.
Describing Mr Johnson as not only a boss but “also a friend”, Mr Raab said: “All of our thoughts and prayers are with the prime minister at this time, with Carrie, and with his whole family.
“And I’m 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 at the helm, leading us through this crisis in short order.”
The Queen and other senior royals sent messages to Mr Johnson’s family and his pregnant fiancee, Carrie Symonds, saying they were thinking of them, and wished the PM a full and speedy recovery.
Latest on lockdown
A ban on public gatherings of more than two people and the closure of shops selling non-essential goods were among the series of restrictions announced by Mr Johnson on 23 March to tackle the spread of coronavirus.
He had said a relaxation of the rules would be considered in three weeks, which would be 13 April.
But on Tuesday, Downing Street suggested that the review would not go ahead on the scheduled date and would instead take place after the three-week mark.
Mr Argar told BBC Breakfast on Wednesday: “We need to start seeing the numbers coming down and that’s when you’re in the negative.
“That’s when you have a sense when that’s sustained over a period of time, that you can see it coming out of that. We’re not there yet and I don’t exactly know when we will be.”
Ahead of a spell of sunny weather forecast in some parts of the UK later this week, Mr Argar urged people to stay at home “however lovely the weather this Easter weekend”.
“If we are, as the statistics appear to show, making a little bit of progress, now’s the time to hold to it,” he said.
According to the government’s coronavirus legislation, the health secretary must review the need for restrictions at least once every 21 days, with the first review to be carried out by 16 April.
Mayor of London Sadiq Khan told BBC Radio 4’s Today programme: “I think we’re nowhere near lifting the lockdown.
“We think the peak – which is the worst part of the virus – is still probably a week and a half away.”