Chinese state media say 17 people were killed and three seriously injured when a long-distance bus overturned and plunged down a deep ravine.

The official Xinhua News Agency said the accident occurred early Wendesday and it was not immediately clear what caused the crash.

The report said 45 people were on the bus, which was headed from eastern Jiangsu province to the coastal city of Xiamen in Fujian province. It overturned in Fujian's Ningde city.

Road safety is a serious problem in China, with many accidents caused by poorly maintained roads and bad driving habits.

Fifteen people were killed when a bus crashed into a ravine in northern Shanxi province in February.