In recent years, the region has been quiet, but in 2009 almost 200 people died in race riots in the capital of Urumqi, which saw ethnic Uighurs fight against Han Chinese.
At least 12 people have been killed in riots in western China, according to state media.
A mob armed with knives attacked victims outside the city of Yecheng, in the Xinjiang region, early yesterday (Tuesday) evening. Xinhua state news agency said the rioters had killed 10 people, and that police had shot two of them dead.
The riot broke out on the opening day of a 3.64 billion yuan (pounds 364million) highway linking Yecheng to Kashgar, 155 miles away. Yecheng is a main entry point for Han Chinese migrants into western Xinjiang, and is also one of the closest points in China to the borders with Afghanistan and Pakistan.
For years, Beijing has said it is fighting terrorists who want to separate Xinjiang from Chinese rule. Between 1990 and 2003, according to state media, more than 300 terrorists escaped through Yecheng into Pakistan.