Prince Charles paid tribute to health service staff as he officially opened the new Nightingale hospital in London.
The facility - the first of the government's emergency field hospitals to treat coronavirus patients - is based in London's ExCel Centre.
The location was only announced to the public on March 24, with the site transformed in just nine days.
Charles sent a video message from his home on the royal Balmoral estate in Scotland to yesterday's opening.
Speaking following seven days of self-isolation after being diagnosed with the virus, he called it "a spectacular and almost unbelievable feat of work".
"It shows how the impossible could be made possible and how we can achieve the unthinkable through human will and ingenuity," he said.
Charles added: "In this dark time, this place will be a shining light."
Also at the ceremony were Health Secretary Matt Hancock, England's chief nursing officer Ruth May, and the head of NHS Nightingale, Prof Charles Knight.
Mr Hancock said the facility was "testament to the work and the brilliance of the many people involved".
It showed the "best of the NHS", he added.
"In these troubled times with this invisible killer stalking the whole world, the fact that in this country we have the NHS is even more valuable than before," he said.
Ms May, meanwhile, paid tribute to all the health service staff working through the darkest of times.
"They know that this is the greatest global health emergency and I am grateful, personally grateful, for everyone that's stepping up to support the NHS right now," she said.
"I know as a nurse myself that, in our time of need, it's important that we are there to serve our patients.
"And I am grateful for them all doing that day in, day out."
Ms May said it was "absolutely fitting" that the hospital was named after Florence Nightingale, who was an "iconic nursing leader of her time" and a "pioneer for infection control".
A combination of NHS staff, contractors and up to 200 military personnel took part in construction.
It is the first of several Nightingale hospitals planned across the UK.
Earlier this week it was announced that Belfast City Hospital's tower block will become Northern Ireland's first Nightingale hospital.
It will become a 230-bed unit for critically ill patients.
The Department of Health is assessing the potential of the Eikon Centre at Balmoral Park, Maze as a second Nightingale facility. This would further increase bed capacity later this year for any further wave of coronavirus.
In Scotland, a temporary hospital is being built at Glasgow's Scottish Events Campus, and in Wales the Principality Stadium in Cardiff will be a field hospital.
Other locations in England include Manchester, Birmingham and Bristol.