Boris Johnson has spent the night in intensive care after his coronavirus symptoms worsened.
The Prime Minister was admitted to St Thomas’ Hospital in London on Sunday after his Covid-19 symptoms persisted for ten days.
Johnson, 55, is understood to be conscious and was moved to intensive care at about 7pm on Monday as a precaution should he require a ventilator.
World leaders including US president Donald Trump and his French counterpart Emmanuel Macron offered the PM their best wishes.
First Minister Nicola Sturgeon and other Scottish and UK political leaders also said their thoughts were with Johnson and his family.
Foreign secretary Dominic Raab will “deputise” for the Prime Minister, whose pregnant fiance Carrie Symonds, 32, is recovering from coronavirus symptoms herself.
Raab said there was an “incredibly strong team spirit behind” Johnson and that ministers were determined to carry out his “direction”.
“The government’s business will continue,” he said.
“The Prime Minister is in safe hands with that brilliant team at St Thomas’ Hospital, and the focus of the government will continue to be on making sure that the Prime Minister’s direction, all the plans for making sure that we can defeat coronavirus and can pull the country through this challenge, will be taken forward.”
He added: “There’s an incredibly strong team spirit behind the Prime Minister, and making sure that we get all of the plans the Prime Minister’s instructed us to deliver, to get them implemented as soon as possible.
“And that’s the way it will bring the whole country through the coronavirus challenge that we face right now.”
The Queen has been kept informed by Downing Street about the Prime Minister’s condition, Buckingham Palace said.
A Palace spokesman said: “Her Majesty has been kept informed by No 10.”
Johnson is the 14th prime minister of the Queen’s reign.