Boris Johnson is breathing without a ventilator and has not been diagnosed with pneumonia, Downing Street has said.

His spokesperson said the PM was stable overnight and remains in good spirits.

Mr Johnson spent the night in intensive care after his symptoms of COVID-19, the disease caused by the coronavirus, worsened and he suffered breathing difficulties.

He  was admitted to St Thomas' hospital in Westminster on Sunday after his coronavirus symptoms persisted for 10 days.

But, having been in hospital for tests and observation, his doctors advised that he be admitted to intensive care.

Tonight there will be a nationwide #ClapForBoris, similar to the support being shown to those working in the NHS in recent weeks the clapping will start at 8pm.

The Prime Minister was transferred to the intensive care unit at St Thomas' Hospital in London on Monday evening as what was said to be a "precaution" in case he needed to be put on a ventilator.

Senior Cabinet minister Michael Gove said Mr Johnson has received "oxygen support" but is not on a ventilator.

"He is kept, of course, under close supervision," he told LBC radio.

"By being in intensive care, if there is further support he needs, it is there at hand.

"But the Prime Minister has not been on a ventilator."

Foreign Secretary Dominic Raab will "deputise where necessary", a Number 10 spokesman said.

A Number 10 spokesman said last night: "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."

It came just a few hours after Mr Raab told a press briefing that the PM remained in charge of the Government despite remaining under observation.

The Conservative Party leader is understood to be conscious and has been moved to the ICU at about 7pm as a precaution should he require ventilation to aid his recovery.

At a press conference less than two hours before the decision was made, Mr Raab told a press briefing that the PM remained in charge of the Government despite remaining under observation.

The Prime Minister is "extremely sick" - with many coronavirus patients who need intensive care requiring invasive ventilation, an expert has said.

Derek Hill, professor of medical imaging at University College London (UCL), said the PM could begiven a breathing aid known as continuous positive airway pressure (CPAP), which bridges the gap between an oxygen mask and full ventilation.

CPAP uses pressure to send a blend of air and oxygen into the mouth at a steady rate, thereby boosting the amount of oxygen that enters the lungs.

But Prof Hill said many Covid-19 patients eventually "progress to invasive ventilation".

This is for people whose illness is so severe they are struggling or unable to breathe for themselves.

A mechanical ventilator either does all the breathing for the patient, or assists the patient's own breathing.

The patient is heavily sedated while a device called an endotracheal tube (ET) is guided through the mouth into the windpipe.

Heavy sedation is then continued because having a tube in the throat can be very uncomfortable.

Patients can be fed at the same time through a tube going into their stomach via their nose.

Prof Hill said it was unclear whether Mr Johnson was breathing on his own, or with the help of a ventilator.

He added: "One of the features of Covid-19 in all countries seems to be that many more men become seriously ill than women - especially in the over 40 age group.

"Also we know that people under about 60 seem to have a higher chance of making a recovery from critical illness with Covid-19 than older people.

"But there is no doubt this turn of events means Boris Johnson is extremely sick.

"It illustrates three of the important healthcare needs of Covid-19.

"Firstly, many patients need help breathing, and there is a shortage of the mechanical ventilators that can do this - and in particular a shortage of the high quality intensive care ventilators most suitable for Covid-19 patients who might need help breathing for over a week.

"Secondly, Covid-19 patients need a huge amount of oxygen to help them breathe - which is potentially going to be in short supply.

"Thirdly, looking after people in intensive care requires skilled staff, and the experience of New York has been that finding enough skilled staff has been the greatest challenge."

The Prime Minister, who celebrated his 55th birthday last June, could also have blood and samples from his throat collected according to guidance issued to doctors by the the World Health Organisation (WHO) last month.

The health body says around 14% of Covid-19 patients will develop symptoms severe enough to need oxygen therapy, and 5% will need intensive care treatment.

The Prime Minister is likely to have already undergone several tests to check his oxygen levels, white blood cell count, and liver and kidney function before he is released from hospital following his admission over Covid-19, according to doctors.

He is also likely to undergo an electrocardiogram to check his heart.

GP Dr Sarah Jarvis told the BBC shortly after he was admitted on Sunday that Mr Johnson would also have his chest X-rayed and lungs scanned, particularly if he was found to be struggling for breath.

The death rate of those admitted to intensive care in the UK with Covid-19 has topped 50%, according to the latest figures.

The figure comes from data compiled by the Intensive Care National Audit and Research Centre (ICNARC) based on a sample of 2,249 coronavirus patients.

The data showed of the 690 patients in the sample whose care outcomes were known, 346 - 50.1% - had died, while 344 had been discharged.

The remaining patients, 1,559, were reported still to be in critical care.

The data shows that of 2,248 patients, 73% were men and 27% were women.