BEIJING - Thirteen people were killed and 41 injured in northern China when a bus plunged off a mountain road into a valley, state-run Xinhua news agency reported on Saturday.

The accident occurred Friday afternoon in Shanxi province as the bus wound along a mountainous highway near the city of Yangquan, the report said.

It said ten passengers died on the spot while three others succumbed to injuries as they were being taken to hospital.

Forty-one people were being treated for injuries sustained in the crash, with three in critical condition and six others in serious condition, it said, quoting the Yangquan city government.

The bus had been hired by a Shanxi healthcare company to take customers on a trip as a reward for using its products, Xinhua said.

It said light rain was falling in the area at the time of the accident but that authorities were still investigating the cause of the crash.