Questions remain over the UK's coronavirus strategy in the absence of Boris Johnson as the prime minister spent a second night in intensive care.
Mr Johnson's condition on Tuesday night remained "stable" as he stayed in St Thomas's for "close monitoring", according to Downing Street.
Speaking on Wednesday morning, health minister Edward Argar added that the PM had not needed mechanical ventilation despite being given oxygen when initially admitted.
While Mr Johnson was said to be still in "good spirits", concerns were raised over when the lockdown measures will be reviewed.
- Health Minister Edward Argar says PM is in a "comfortable and stable" condition:
Health Minister Edward Argar confirmed on Wednesday that Mr Johnson was in a "comfortable and stable" condition in ICU and added that the prime minister was "in good spirits".
As Foreign Secretary Dominic Raab arrived at Number 10 for his second day deputising for the PM, Mr Argar told ITV News:
"The Government is united behind the strategy the prime minister has set out for tackling this virus united behind him and behind Dom [Dominic Raab] to make sure we deliver for the people of this country in beating this virus".
It comes as England's chief medical officer admitted the UK has "a lot to learn" from Germany's expansive testing scheme.
But there was cautious optimism from chief scientific adviser Sir Patrick Vallance after he said the fight against Covid-19 "could be moving in the right direction".
- What happens in an intensive care unit? Watch below
Meanwhile the first of the NHS Nightingale hospitals, at London's ExCel centre, received its first patients on Tuesday.
The Nightingale was built to boost treatment capacity in London but officials stressed that limits had not been reached at other sites across the capital.
"There is also treatment capacity available in other hospitals across London to complement the care being provided at the London Nightingale," an NHS Nightingale London spokesperson said.
The admissions come just two weeks after the temporary hospital with a planned capacity of 4,000 was formally announced, but later than had initially been expected.
Later on Tuesday night, President Donald Trump claimed that the UK called the US with an urgent plea for 200 ventilators, as ministers seek to scramble to boost capacity for the sickest of patients.
"We're going to work it out, we've got to work it out," he said.
"They’ve been great partners. They wanted 200, they need them desperately."
Earlier at Tuesday's daily Downing Street press conference, Foreign Secretary Dominic Raab said he is "confident" the PM will pull through after a worsening of his coronavirus symptoms.
Mr Raab, who is deputising in Mr Johnson's absence, suggested the review of the lockdown announced by the PM when he set out the restrictions would not go ahead on Monday as scheduled.
He stressed that they could not consider easing the lockdown restrictions until it was clear the peak of the epidemic had passed and it could be "responsibly done".
Downing Street later confirmed the review would take place after the three-week mark originally committed to.
But the emergency legislation laid before Parliament three days after the PM's announcement states that a review must take place every 21 days, with the first deadline being April 16.
Sir Patrick said there were signs that the rates of new infections and new hospital admissions for Covid-19 were "flattening off".
But he added it would be another "week or so" before they could be sure, indicating lockdown measures would not be eased before then.
Professor Chris Whitty, the chief medical officer for England, said the UK needed to learn from the example of Germany where the number of deaths appeared to be growing more slowly.
"We all know that Germany got ahead in terms of its ability to do testing for the virus and there's a lot to learn from that and we’ve been trying to learn the lessons from that," he said.
Updating the nation on the PM's condition, Mr Raab said he remained stable and had not required a ventilator but had received "standard oxygen treatment" while breathing without assistance.
"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," he said.
He said that ministers would not "blink or flinch" from following the instructions Mr Johnson had set out before he was admitted to hospital.
But he appeared reluctant to say whether he would be prepared to take a decision to break with the PM's strategy while he was still in hospital if he believed a change of direction was necessary.
"He's asked me to deputise for him for as long as is necessary, but the normal Cabinet collective responsibility and principles that inform that will apply," he said.
The latest official figures from the Department of Health showed that 6,159 patients have died in hospital after testing positive for coronavirus in the UK as of 5pm on Monday – an increase of 786 on the previous day.
However, Sir Patrick said there were signs the number of new cases "could be moving in the right direction".
"It's possible that we’re beginning to see the beginning of change in terms of the curve flattening a little bit. We won’t know that for sure for a week or so," he said.
Coronavirus: Everything you need to know