The Chinese state news agency says 41 people have died in a bus fire in central China.

The official Xinhua News Agency said the sleeper coach burst into flames along a highway in Henan province early Friday local time. Only six of the 47 people on board managed to escape.

The rest were burned beyond recognition and will have to be identified using DNA.

Xinhua said it was unclear what caused the blaze and that an investigation was under way.

Serious traffic accidents are common in China due to lax driving habits, overloaded vehicles and bad road conditions. Earlier this month, 23 people died when a speeding truck rammed into a tourist bus that was illegally stopped in a highway emergency lane in central China’s Hubei province.