Four people were killed and six more injured after a police van veered off the road and plunged into a river in southwest China's Guizhou Province early on Monday.

One more rider was missing in the highway accident that occurred around 5:30 a.m. on No. 308 provincial highway in Leishan County, said provincial transportation authorities.

The van, which belonged to the county's public security bureau, was heading for Guiyang, the provincial capital, carrying 11 people aboard who were said to be on their way to perform a duty.

The four were killed on the spot.

Cause of the accident is being investigated.