Prime Minister Boris Johnson has been moved into intensive care after his coronavirus symptoms worsened, Downing Street has confirmed.
The 55-year-old has been battling COVID-19 since late last month and yesterday was admitted to hospital as a precautionary measure.
Johnson had been communicating with other members of the government from his hospital bed earlier today but his conditions worsened over the course of the day.
In a statement, Number 10 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."
Johnson is thought to still be conscious and not using a ventilator at this point.
The newly-appointed leader of the Labour party, Sir Keir Starmer, wrote on Twitter: "Terribly sad news. All the country's thoughts are with the Prime Minister and his family during this incredibly difficult time."
Johnson's pregnant fiancée Carrie Symonds has been isolating away from the PM for the past fortnight and has been showing coronavirus symptoms herself.
Chancellor of the Exchequer Rishi Sunak said: "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."
Former PM Theresa May wrote: "My thoughts and prayers are with @BorisJohnson and his family as he continues to receive treatment in hospital. This horrific virus does not discriminate. Anyone can get it. Anyone can spread it. Please #StayHomeSaveLives"
More than 1.3 million people have now tested positive for COVID-19 worldwide, including 51,608 in the UK.