UK Prime Minister Boris Johnson was moved to an intensive care unit on Monday after his condition with coronavirus symptoms "worsened," his office has said.

Johnson, 55, was first admitted to St Thomas’ Hospital in London on Sunday evening for what he said were “routine tests,” saying on social media that he was in “good spirits.”

But the apparent change in the leader’s health has shocked the nation, with politicians from his party and the opposition voicing their support for the leader, as the country battles an outbreak that has killed more than 5,000 people.

“Over the course of this afternoon, the condition of the Prime Minister has worsened and, on the advice of his medical team, he has been moved to the Intensive Care Unit at the hospital,” a Downing Street spokesperson said.

According to Downing Street officials, Johnson remains conscious and has been moved to the intensive care unit as a precaution, in case he requires ventilation.

The move strikes a sharp contrast to earlier reports on Johnson’s condition: During his period of self-isolation, Downing Street had said that Johnson’s symptoms were “mild,” and on Sunday said his hospitalization was just a “precautionary step.”

The Prime Minister’s spokesperson had said earlier on Monday that Johnson spent a “comfortable” night in hospital, but would not comment on reports Johnson was given oxygen.

Officials are no longer describing his symptoms as mild.

Foreign Secretary Dominic Raab, who is the First Secretary of State and the most senior Cabinet minister, said Johnson had asked him to deputize for the leader where necessary.

Raab chaired Monday’s regular morning coronavirus briefing and made a televised statement saying that the government will continue Johnson’s direction in responding to the outbreak.

The United Kingdom’s death toll of above 5,000 is one of the highest in the world. The government has been scrambling to implement widespread testing as evidence grows that asymptomatic people could carry and spread the virus.

Before being moved to intensive care, Johnson had said he was keeping in touch with his team and thanked staff at Britain’s National Health Service for taking care of him.