Top resorts including Val d'Isere, Courchevel and Tignes are among those hit in the strike, which stretches from the Alps to the Pyrenees.

French police have invoked special powers to order at least one doctor to remain on duty at each resort site.

The doctors are demanding extra pay for treating sprains. They claim that they are spending hours dealing with sprains but can claim only 20 euros (£13) for each patient.

We are doing the same work as in emergency wards, with the same X-ray procedures and all, but social security doesn't recognise this Jean-Dominique Laporte Mountain doctors' group

Doctors' representatives said the strike call had been heeded by most doctors.

"Ninety percent of the clinics are closed, across all the mountains," said the head of the Association of Mountain Doctors, Marc-Herve Binet.

Another week-long stoppage could be called in January unless a solution was found, he said.

Talks with health ministry officials had to result in a "rapid and intelligent" agreement, said Mr Binet.

Casualty list

The doctors say sprains take as long to deal with as fractures, and they must be given the right to earn more for treating them.

Around 67,500 people a year suffer sprains while skiing in France - around 45% of the total number of skiing accidents recorded every year.

"We are doing the same work as in emergency wards, like at the hospital, with the same X-ray procedures and all, but social security doesn't recognise this," said doctors' representative Jean-Dominique Laporte.

In a separate dispute, gynaecologists and obstetricians say they will stop delivering babies and carrying out surgery in private clinics on Wednesday, in protest against rises in compulsory medical insurance.

And casualty ward doctors are also threatening to go on strike later in January.