LANZHOU, Jan. 9 -- Nine people were killed and four others injured after a truck carrying 13 people plummeted off a road in northwest China's Gansu Province, traffic police said Thursday.

The truck driver lost control and the vehicle plunged 20 meters into a ditch in Gangu County, Tianshui City, at around noon on Thursday, said provincial traffic police and work safety authorities.

The passengers were family members who were on their way back from a funeral.

Police said low-speed cargo trucks are banned from carrying passengers. They are investigating the cause of the accident.