French police have launched an investigation into the mysterious recovery of two bare human legs on two beaches on the Atlantic coast.

A walker alerted authorities after he spotted one limb on the La Linière beach on the island of Noirmoutier, in the western Vendée province.

Police searching the area found the second leg on the nearby Souzeaux beach, a source close to the investigation told AFP.

"Clearly these remains were washed ashore by the sea, where they had remained for quite some time," the source said.

Prosecutors in the Vendée sub-prefecture of Les Sables-d'Olonne told Le Figaro the two legs belong to the same person - a white man aged between 20 and 50 - and had remained in the water for about a month.

The first human remain to be found was a leg section going from the mid-thigh to the mid-calf. The second was the whole leg but with no foot attached.

The limbs were sent to forensics in Nantes for DNA tests.

The island of Noirmoutier is a popular tourist destination famous for its sandy beaches.

It is connected to the mainland by a natural bridge known as the Passage de Gois, which is flooded by the high tide twice a day.

The picturesque location has been often used to host a stage of the Tour de France cycling race.