Six students have been killed in a collision between a school bus and another vehicle in a town on France's Atlantic coast.

Rochefort mayor Herve Blanche said the circumstances of the early morning crash are under investigation, and confirmed that six children had died.

France's transport minister and other government officials are heading to the scene of the crash in the Charente-Maritime region.

Eighteen adolescents were on the bus at the time of the collision with a truck.

Jerome Servolle, a police union official in the town, said a gate-like object swung open on the truck, slicing through the school bus at window height.

"The word chaos is not strong enough. This is such a tragedy," he said.