Dominic Raab has paid tribute to "fighter" Boris Johnson as the UK's coronavirus death toll soared by 786 to 6,159.
The Foreign Secretary says his boss is "receiving the very best care" and remains in good spirits after spending the night in intensive care.
The Prime Minister was moved to intensive care on Monday night following a worsening of his Covid-19 symptoms.
Johnson is “stable” in hospital and is in “good spirits” but remains in intensive care, Downing Street has said.
Speaking at today's coronavirus daily update, Raab said: "He is not just the Prime Minister. For all of us in Cabinet, he is not just our boss.
"He is also a colleague and he is also our friend. So all our thoughts and prayers are with the Prime Minister at this time, with Carrie (Symonds) and his whole family.
"And I'm confident he will pull through because if there is one thing that I know about this Prime Minister is he is a fighter and he will be back leading us through this crisis in short order."
Raab, the Foreign Secretary and First Secretary of State, told the daily Downing Street press conference: "He's receiving the very best care from the excellent medical team at St Thomas's Hospital.
"He remained stable overnight.
"He's receiving standard oxygen treatment and breathing without any assistance, he's not required any mechanical ventilation or non-invasive respiratory support.
"He remains in good spirits and in keeping with usual clinical practice his progress continues to be monitored closely in critical care."
Raab is standing in for the Prime Minister "whenever necessary", including leading the daily meetings of the coronavirus "war cabinet".
When asked about reviews into lockdown restrictions, Raab told how the Raab says the government is "not at the stage" to make changes as there is not enough reliable data to say whether the measures are working.
During the daily briefing from Downing Street, Chief Scientific Adviser Sir Patrick Vallance also confirmed that over 1,900 people in hospital are taking part in clinical trials.
He says we may be be starting to see the beginning of hospital admissions flattening, as there has been no accelerated take-off.
However, Sir Patrick advised we won’t be able to know for sure for a week or so.
Sir Patrick told the conference: "It does begin to suggest that things might be moving in the right direction.”
He added that the "uptick" in the number of deaths is normal, but says the UK is "on track" compared to other countries.
Meanwhile it was revealed care home deaths are not being included in official figures, and that we can expect to see the total rise as a result.
The total number of people in the UK tested for coronavirus since the outbreak began - 213,181, as of 9am on April 7 - is the equivalent of around 320 people in every 100,000, or 0.3% of the population.
The number cannot be compared with the equivalent total from yesterday because the figures are missing data from Manchester and Leeds due to a processing delay.
The difference between the number of new deaths announced today by the D epartment of Health - 786 - and the combined total of new deaths announced today by health authorities in the four nations of the UK - 854 - is due to the difference in how and when the data is collected and reported.
Neither of these figures is an accurate measure of how many deaths have occurred in the UK since yesterday.
For example, one of the deaths announced today by NHS England took place nearly three weeks ago on March 19.
296 people have now died from coronavirus in Scotland - an increase of 74 deaths overnight.
The number of confirmed cases has risen to 4,229 up 268 from Monday.
A total of 199 Scots are in intensive care receiving treatment, it has been confirmed.
Of the confirmed positive cases, 1751 people are in hospital which is an increase of 152.
