The area is known in Chinese as Yutian, and in the local Uighur language as Keriya. The China Earthquake Networks Center measured the quake at magnitude 7.3 and said it was followed by at least seven smaller quakes within the following half hour.
Yutian county is a mountainous area several thousand meters above sea level on the edge of the Taklamakan desert.
The director of the Yutian Civil Affairs Bureau, Zhang Chong, said officials were still gathering information. A police officer in Yutian said he had felt tremors shaking the police station and ran outside.
Wang Gang, a fire brigade chief in Yutian County, told the national CCTV broadcaster he was heading from the county seat to the earthquake zone, about 100 kilometers (62 miles) away, with a team of police and firefighters.
A magnitude 7.2 quake in that area in March 2008 collapsed some houses but caused no injuries.
China's worst earthquake in recent years was a magnitude-7.9 temblor that struck the southwestern province of Sichuan in 2008, leaving about 90,000 people dead or missing.