NANNING - Four people?were killed and another six injured in a six-vehicle pile-up on a national highway in South China's Guangxi Zhuang autonomous region on Saturday afternoon, according to an announcement by local authorities.

The accident happened at around 1 pm on a section of the No 210 National Highway in Nandan county in the city of Hechi when a truck which was followed by four sedans overturned and collided with another truck coming from the opposite direction, said local traffic police.

The six injured, one of whom is in critical condition, have been rushed to a local hospital.

As some people remain trapped in the vehicles involved in the accident, the exact number of casualties has still not been confirmed.

Rescue work is ongoing and an investigation into the cause of the accident is under way.

The pile-up has caused a 6-km-long traffic jam on the highway so far.