A further 24 people were injured, 14 critically, when the coach smashed through a roadside barrier on the steep Laffrey gradient, some 30km from the southeastern city of Grenoble, after apparently suffering braking problems.

Most of the victims perished in the fire, said emergency officials, and DNA forensic experts from Paris would be needed to identify the bodies.

Reports said the Poles, from the Szczecin area of northwest Poland, had been due to return home on July 24 after two weeks of pilgrimage in Spain and France.

French Prime Minister Francois Fillon, who visited the crash site, said the Polish coach did not appear to have a permit for the dangerous stretch of road, a rule imposed after a spate of crashes in the 1970s left scores dead.

Investigators are expected to focus on the braking system and speed of the coach, and will want to speak to the backup driver who survived the smash.