The new infection was found in a 50-year-old man who had shared a hospital room with France's only other known sufferer, the ministry said in a statement.

Health experts are concerned about clusters of the new coronavirus strain, nCoV, which was first spotted in the Gulf and has spread to France, Britain and Germany.

There has so far been little evidence of direct and sustained human-to-human transmission of nCoV - in contrast to the pattern seen in the related Severe Acute Respiratory Syndrome (SARS) virus, which killed 775 people in 2003.

The first nCoV case in France, confirmed on May 8, is a 65-year-old man who fell ill after returning from Dubai late last month.

Both French patients are in hospital in the northern city of Lille, where the younger man was transferred to intensive care on Sunday as his breathing deteriorated.

His case suggests that airborne transmission of the virus is possible, though still unusual, said Professor Benoit Guery, head of the Lille hospital's infectious diseases unit.

"Fortunately, this remains a virus that is not easily transmitted," Guery told the BFMTV channel. "I don't think the public should be concerned - it has been out there for a year and we have 34 cases globally."

He said the second French case had occurred because the first patient presented "quite atypical" symptoms and had not been isolated immediately.

Health officials screened 124 people who had come into contact with him and carried out laboratory tests on at least five, including three medical staff.

All came back negative except the fellow patient, who had been in "close and prolonged contact" when they shared a hospital room in nearby Valenciennes between April 27 and 29, the ministry said.

French authorities are now broadening the screening effort to include anyone who has been in contact with the second confirmed case.

(Reporting by Nicolas Delame; writing by Laurence Frost; Editing by Kevin Liffey)