SHANGHAI _ A bus plunged off a mountain road in southwest China, killing 12 people and injuring eight others, official media reported Monday.

The bus was carrying 20 people deep in the hills of Guizhou province when it crashed through a guardrail and into a 10-meter (33-foot) deep culvert on Sunday afternoon, the Xinhua News Agency said.

It said 11 people died at the scene and another died in a hospital.

The cause of the crash wasn't given and Xinhua said the driver remained in a coma. Such accidents are often blamed on poorly maintained or overloaded vehicles, along with speeding and exhausted and inattentive drivers.