Coronavirus patients have been admitted to the new NHS Nightingale Hospital for the first time.
The temporary 4,000-bed facility was built in just nine days at the ExCeL Centre in east London, and it will need up to 16,000 staff to keep it running.
Those admitted to the hospital will already be on a ventilator and will remain there until their treatment is finished.
A spokeswoman has declined to say exactly how many coronavirus patients have been admitted so far – but stressed “there is also treatment capacity available in other hospitals across London”.
NHS Nightingale has more than 80 wards containing 42 beds each, and COVID-19 patients are being transferred from intensive care units elsewhere in the capital.
Those also suffering from other serious conditions such as cardiac issues will be cared for at other specialist centres.
Contractors and about 200 military personnel worked to get it running in just over a week, with NHS chief executive Simon Stevens describing their efforts as “nothing short of extraordinary”.
Healthcare staff will be able to sleep at nearby hotels once they complete their shift, or they can choose to go home.
The facility was announced just two weeks ago, but the admissions are later than had been initially planned.
Other Nightingale hospitals are due to open in Bristol, Harrogate, Birmingham and Manchester.
On Tuesday, it was confirmed that another 786 patients have died in the UK after contracting the coronavirus – bringing the total to 6,159.
But there was cautious optimism from chief scientific adviser Sir Patrick Vallance, who said the fight against COVID-19 “could be moving in the right direction”.
Sir Patrick said there were signs that the rate of new infections and hospital admissions for coronavirus were “flattening off” – but he cautioned that it will take another week to be sure.
Meanwhile, Donald Trump has claimed that the UK has made an urgent plea to the US for 200 ventilators as ministers scramble to boost capacity for the sickest of patients.
“We’re going to work it out, we’ve got to work it out,” the president said. “They’ve been great partners. They wanted 200, they need them desperately.”
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Prime Minister Boris Johnson has spent a second night in intensive care after testing positive for coronavirus 12 days ago.
Downing Street said the 55-year-old was suffering from “persistent” symptoms of COVID-19, including a cough and a high temperature.
On Tuesday, his stand-in Dominic Raab said the prime minister remains stable and has not required a ventilator – adding he has received “standard oxygen treatment” while breathing without assistance.