At least six people were killed and another five injured in a 31-vehicle pileup on the Beijing-Tibet Expressway in north China's Inner Mongolia Autonomous Region that occurred on Thursday morning, according to local traffic police.

Thirty-one cargo trucks rear-ended each other on a 2-km-long section of the expressway in Xinghe County. Most of the vehicles were semitrucks loaded with coal, according to local police.

The injured have been taken to a local hospital.

The accident led to 40 km of the expressway becoming congested. Traffic police are still clearing the site; traffic has yet to be resumed.

An investigation into the accident is under way.