The field hospital, a temporary structure of tents usually employed to assist the wounded in a war zone, has been erected in the eastern French city of Mulhouse where the intensive care unit of the main hospital has been overwhelmed by coronavirus cases.
Armed Forces Minister Florence Parly told parliament that the field hospital could admit up to 30 patients in intensive care and had now already admitted its first patient.
Construction of the hospital began on Saturday in a parking lot next to the main hospital in Mulhouse. It will be reserved for severe coronavirus cases that need respiratory help.
The construction of such a facility, usually used in war, in mainland France during peacetime is unprecedented.
The Haut-Rhin region in eastern France where Mulhouse is located has been one of the worst hit in the country by the coronavirus, after many people were infected during an evangelical church meeting in the city in February.
In another hugely unusual move, France will on Wednesday use a specially set-up TGV high speed train to evacuate 30 coronavirus patients from the east to other parts of France, Health Minister Olivier Veran announced.
Smaller numbers have already been evacuated from the overwhelmed hospitals of the east by air to other locations in France and also over the border into Germany or Switzerland.