Chinese police and a state news agency say a passenger plane flying from a restive western region to Beijing has made a forced landing after an anonymous threat was received.

A Lanzhou city police official surnamed Shi says the plane made an emergency landing at Lanzhou airport on Monday afternoon.

The official Xinhua News Agency cited posts on popular microblogs as saying the plane left Urumqi, the capital of the restive Xinjiang region.

Xinhua says all passengers have been taken off the plane and police are investigating.

Xinjiang is home to the traditionally Muslim Uighur ethnic group. Long-simmering resentment among Uighurs over rule by China's Han majority has sporadically erupted into violence.