Work safety authorities blamed overcrowding and illegal operation for an automobile accident that killed 18 people and injured 16 others in north China's Hebei Province on Aug. 28.

The accident happened around 5 a.m., when a bus loaded with 34 migrant workers rear-ended a semi-truck trailer parked on the side of a road near the city of Zhangjiakou. The trailer pulled over to the side of the road without turning on its hazard lights, while the bus failed to maintain a safe speed before colliding with the trailer, according to a report released on Thursday by a work safety committee under the State Council, or China's cabinet.

The bus was designed to carry 17 passengers and was not registered with local police, according to the report. In addition, the driver of the bus was driving illegally and using fake license plates, the report said.

The work safety committee will supervise further investigations into the accident and publicize the results as soon as possible, according to the report.