He is not believed to be on a ventilator and is receiving “close supervision” at St Thomas’ Hospital in London, according to Cabinet minister Michael Gove.
Speaking to LBC, a British radio channel, Gove said: “He is not on a ventilator. The prime minister has received some oxygen support.
“He is kept, of course, under close supervision. By being in intensive care, if there is further support he needs, it is there at hand.
“But the prime minister has not been on a ventilator,” said Gove, who self-isolated on Tuesday after a family member showed symptoms of COVID-19.
Johnson was moved to an intensive care unit on Monday night after his condition “worsened”, a Downing Street spokesman said, adding that he had asked Foreign Secretary Dominic Raab to deputise “where necessary”.
He was initially admitted to hospital on Sunday due to persistent symptoms of COVID-19, which he was diagnosed with more than a week ago.