Two knife-wielding men hijacked a truck and killed its driver, before ramming the vehicle into a crowd and getting out and attacking the pedestrians, leaving seven people dead and 22 injured in northwest China, a police official said Sunday.

The attack happened in the Silk Road city of Kashgar in northwest Xinjiang, a region rocked by ethnic violence in recent years.

State-run Xinhua News Agency reported that two blasts were heard about an hour before the incident Saturday night - one from a minivan and the other from the food stall-lined street where the hijacking took place. The police official, from the information office of the Xinjiang regional public security bureau, said she could not confirm whether there were explosions.

According to the official, two men hijacked a truck and stabbed the driver to death. The men then drove the truck into a crowd, got out of the vehicle and attacked people along the road with a knife or knives, said the official, who refused to give her name, as is common with Chinese officials.

During the fracas, one of the suspects was killed and the other caught, the official said.

A total of seven people died and 22 were injured, she said. Xinhua said six bystanders and one suspect were killed.

The official said the case was under investigation and that the motive was unclear.