Good Morning Britain host Piers Morgan has slammed critics of Boris Johnson on the night that the Prime Minister moved into intensive care.

Johnson, 55, was admitted to ICU at St Thomas' Hospital in London on Monday evening after his coronavirus symptoms worsened.

Morgan has been critical of the government's response to the pandemic in recent weeks but said that only positive vibes should be directed Johnson's way in light of the worrying development.

"Fight hard Boris - we're all rooting for you," he wrote on Twitter. "If you have nothing positive to say about Boris Johnson on here tonight, then shut the f*ck up. The man is our Prime Minister & he is fighting for his life."

Morgan went on to call upon Downing Street to be fully transparent with the PM's health status in the days ahead.

"Downing Street must now be 100% straight with the media & public re Boris's condition. No more lies," he wrote. "Britain is in a war & he is the Prime Minister. His health is thus a matter of paramount public interest. We must all hope & pray Boris comes through this."

Johnson is thought to have been moved to intensive care as a precautionary measure and is currently breathing without the need for a ventilator.