Boris Johnson has been moved to intensive care after his coronavirus condition worsened, Downing Street announced tonight.
The Prime Minister was transferred to the ICU at St Thomas' Hospital in London at 7pm this evening.
He is conscious and has asked Foreign Secretary Dominic Raab to deputise for him.
Mr Raab, also First Secretary of State, is primed to take charge of the government's coronavirus response, but it is understood he is not a temporary prime minister.
Mr Johnson, 55, was transferred to intensive care as a precaution in case he requires a ventilator.
The PM tested positive for coronavirus 11 days ago and started self-isolating in his Number 11 flat, where he remained at the helm of the UK's war on the virus.
He was last seen looking exhausted on Friday, when he posted a video message on Twitter revealing he was still suffering from a high temperature.
A Number 10 spokesperson said: 'Since Sunday evening, the Prime Minister has been under the care of doctors at St Thomas' Hospital, in London, after being admitted with persistent symptoms of coronavirus.
'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 PM has asked Foreign Secretary Dominic Raab, who is the First Secretary of State, to deputise for him where necessary.
'The PM is receiving excellent care, and thanks all NHS staff for their hard work and dedication.'
Scotland First Minister Nicola Sturgeon tweeted: 'My thoughts are with the PM and his family - sending him every good wish.'
Business minister Nadim Zahawi tweeted: 'Thoughts & prayers for @BorisJohnson & @carriesymonds and their family. I have known Boris for 20 years he is a fighter and will beat this virus.'
Chancellor Rishi Sunak tweeted: 'My thoughts tonight are with @BorisJohnson and @carriesymonds. I know he'll be getting the best care possible and will come out of this even stronger.'
Members of the newly-formed shadow cabinet offered their support for the PM.
Shadow justice secretary David Lammy tweeted: 'Awful news. My very best wishes to the Prime Minister, as well as his partner Carrie, family and friends. Get well soon @BorisJohnson.'
Labour deputy leader Angela Rayner posted: 'Sending my best wishes at this worrying time to the PM @BorisJohnson and @carriesymonds and hoping that his condition stabilises in his battle with £Coronavirus.'
And shadow deputy mental health minister Dr Rosena Allin-Khan tweeted: 'I wish the Prime Minister a full and speedy recovery and thank the NHS team looking after him and everyone at St Thomas'.
'Coronavirus can affect anyone, the symptoms can be really awful. Please, please, remind your friends and family to stay at home!'
Business minister Nadim Zahawi tweeted: 'Thoughts & prayers for @BorisJohnson & @carriesymonds and their family. I have known Boris for 20 years he is a fighter and will beat this virus.'
Chancellor Rishi Sunak tweeted: 'My thoughts tonight are with @BorisJohnson and @carriesymonds. I know he'll be getting the best care possible and will come out of this even stronger.'
Members of the newly-formed shadow cabinet offered their support for the PM.
Shadow justice secretary David Lammy tweeted: 'Awful news. My very best wishes to the Prime Minister, as well as his partner Carrie, family and friends. Get well soon @BorisJohnson.'
Labour deputy leader Angela Rayner posted: 'Sending my best wishes at this worrying time to the PM @BorisJohnson and @carriesymonds and hoping that his condition stabilises in his battle with £Coronavirus.'
And shadow deputy mental health minister Dr Rosena Allin-Khan tweeted: 'I wish the Prime Minister a full and speedy recovery and thank the NHS team looking after him and everyone at St Thomas'.
'Coronavirus can affect anyone, the symptoms can be really awful. Please, please, remind your friends and family to stay at home!'
