Boris Johnson has been taken into the hospital intensive care unit for treatment for coronavirus after his condition worsened, his office said.

The U.K. prime minister was admitted to St Thomas’ Hospital in London on Sunday night because his virus symptoms had not cleared up, and he became more seriously ill on Monday afternoon, a government spokesperson said in an email. He remains conscious and was moved to intensive care at about 7 p.m. in case he needs ventilation to help him recover, an official said.

“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,” the government statement said. Foreign Secretary Dominic Raab will stand in for Johnson running the country, “where necessary.”

The government said Johnson, 55, is receiving “excellent care” and thanked “all NHS staff” for their hard work and dedication.

Johnson announced on March 27 that he was isolating himself after testing positive for coronavirus. On the evening of April 5, unable to shake the symptoms, he was admitted to St. Thomas’ suffering from a “persistent” cough and a fever.

Throughout the day on Monday, his officials insisted the prime minister remained in charge of the government and was continuing to work on his papers while keeping in touch with his team. Reporters raised questions over how seriously ill Johnson was after Raab, the U.K.’s first secretary of state, disclosed that the pair had not spoken since Saturday.

The prime minister’s worsening illness comes at a critical time for the U.K., with scientists predicting the country will suffer the peak of its coronavirus outbreak in the next seven to ten days.

--With assistance from Alex Morales and Olivia Konotey-Ahulu.

This article was provided by Bloomberg News.