CHONGQING - A long-distance bus plunged into a roadside ditch in southwest China Wednesday, killing at least four people and injuring an unspecified number of others, local authorities said.

The bus, carrying 36 people, broke through a guardrail and plunged into a ditch in Wuxi county, located in the municipality of Chongqing, a county government spokesman said.

Local residents rushed to the scene and rescued the passengers from the ditch, the spokesman said.

An unspecified number of injured people were sent to nearby hospitals, and their conditions were described as stable.

Local police are investigating the cause of the accident, the spokesman said.