A gate-like object swung open on a truck, slicing through the bus
At least six children have been killed after part of a truck carrying rubble swung open and raked through their school bus.
The accident happened just after 7.00am local time in the historic town of Rochefort in southwestern France.
Officials say there were 18 people on the bus at the time. Three other children suffered minor injuries.
Jerome Servolle - a police union official - said a gate-like object swung open on the truck, slicing through the bus at window height.
"The word chaos is not strong enough. This is such a tragedy," he said.
President Francois Hollande has offered his condolences to the victims and their families.
He also promised everything possible would be done "to shed light on the causes of this tragedy".
The French minister in charge of transport was apparently heading to the scene.
It comes a day after two children were killed in another accident involving a school bus.
Aged 12 and 15, they died when their vehicle veered off a road in snowy conditions near the Swiss border in eastern France.
The vehicle was carrying 32 children on its daily trip to the village school in Montbenoît.