He was reportedly moved on the advice of his medical team and was receiving ‘excellent care’.
Meawhile, Johnson has asked Foreign Secretary Dominic Raab to deputize ‘where necessary’.
Johnson was admitted to hospital in London with ‘persistent symptoms’ on Sunday evening.
The Queen has been kept informed about Johnson’s health.
The Prime Minister was given oxygen late on Monday afternoon, before being taken to intensive care unit.
However, he has not been put on a ventilator.
Meanwhile, US President Donald Trump said Americans ‘are all praying for his recovery’.
He described Johnson as ‘a very good friend of mine and a friend to our nation’ who is ‘strong’ and ‘doesn’t give up’.
Johnson was initially taken to hospital for routine tests after testing positive for coronavirus 10 days ago.
His symptoms included a high temperature and a cough.
Earlier on Monday, he tweeted that he was in ‘good spirits’.