At least 27 people have been killed and three others injured after knife-wielding gangs rampaged through a town in far western China, according to state media.

China's state Xinhua news agency said mobs attacked police stations, a local government building and a construction site in the Turpan Oasis in the Turkic-speaking Xinjiang region.

Nine police officers and security guards, as well as 8 civilians, were killed before police shot dead 10 of the attackers.

The death toll from the unrest was the worst in the restive region since July 2009, when nearly 200 people were killed in riots in the region's capital Urumqi, involving local predominantly Muslim Uighurs and ethnic Han Chinese.

After violence broke out, search results for the words Xinjiang and Lukqun, in both English and Chinese, were unavailable on Chinese search engines.

The reasons for the attacks were not immediately clear, but Xinjiang is home to a large population of Uighurs and the influx of China's Han majority has led to unrest.

Many Uighurs, who have ethnic links to central Asia, accuse the Chinese government of placing restrictions on their culture, language and religion.

They also claim that Beijing has encouraged the increasing number of Han Chinese in order to reduce their dominance.

In 2011, the China National Petroleum Corp announced it had started large scale exploration of an oil field around Lukqun, thought to be the world's deepest heavy oil reserve.