Four people were killed and nine others injured Tuesday in an expressway pile-up that involved 13 automobiles in northwest China's Xinjiang Uygur Autonomous Region, local authorities said Wednesday.

The accident happened at about 9 p.m. on an expressway that links Turfan with Urumqi, the capital city of Xinjiang, according to the fire brigade in Fukang City.

Low visibility as a result of heavy fog and slippery road after the rain and snow during the daytime were thought to blame for the pile-up accident, sources with the fire brigade said.

The four dead people were from a sedan that was stuck between two other vehicles, according to the sources.

The injured people were sent to a nearby hospital, but their conditions are not available.

Police are further investigating the accident.