French hospitals are being stretched to their limits by a major flu epidemic sweeping the country, France's health authorities warn.

Thousands of mostly elderly people have been admitted due to a winter outbreak of a of the virus known as H3N2.

Health Minister Marisol Touraine told hospital directors Tuesday that the latest figures showed a "worrying" situation with the epidemic yet to reach its peak.

This winter's virus is a cousin of a flu that contributed to 18,000 deaths two years ago, public say.

At the weekend, the health ministry ordered a probe into the deaths of 13 residents of a nursing home in the eastern city of Lyon late last month.