LANZHOU, Jan. 19 -- A small passenger vehicle rear-ended with a heavy-duty semi-trailer in northwest China on Monday morning, leaving six people dead and one injured.

The passenger vehicle ran into the trailer, which parked at roadside for having hit the expressway guardrail earlier, around 5 a.m. on an expressway in Baiyin City, Gansu Province.

Nine people were aboard the passenger vehicle, two more than its approved capacity.

Medical and transport departments have rushed to rescue after the accident occurred. Authorities have also opened probe into the cause of the accident.