Boris Johnson is "responding to treatment" for coronavirus as he spends his third day in hospital.
The prime minister was being kept in St Thomas' Hospital in London "for close monitoring" and remained clinically stable, Downing Street said.
Downing Street said he was not working but could contact those he needed to.
No 10 has also suggested a review of the lockdown measures put in place on 23 March would not go ahead on Monday - the three-week point - as planned.
Asked on BBC Breakfast when the measures might be lifted, health minister Edward Argar said he did not know but added: "We're not there yet."
He said the peak in cases must pass "before we can think about making changes", adding: "It's too early to say when we will reach that peak."
Downing Street said Mr Johnson was in "good spirits" as he continued to receive standard oxygen treatment. He 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.
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.
Foreign Secretary Dominic Raab, who is deputising for Mr Johnson, said on Tuesday he was "confident" the PM would recover from this illness, describing him as a "fighter".