TURPAN, China (AFP) - Armed police in China's ethnically divided Xinjiang blocked the road Thursday to the site of riots that left 27 people dead a day earlier, in the restive region's deadliest violence in years.

Officers stationed 40 kilometres outside Turpan city's Lukqun township checked car passengers' IDs and barred journalists from entering, citing safety concerns.

A visitor in Turpan - which lies about 250 kilometres from the regional capital Urumqi - said he saw another roadblock with armed officers and about 20 police vehicles.

The Xinhua state news agency said Wednesday that "knife-wielding mobs" attacked police stations and other locations, and nine police or security guards and eight civilians were killed before police opened fire.

A resident surnamed Chai said a helicopter arrived on the scene along with many police and soldiers.

Xinjiang is home to around 10 million members of the mostly Muslim Uighur ethnic minority. Many complain of religious and cultural repression by Chinese authorities.

Authorities deny that and have pushed investment in the resource-rich region in an attempt to boost development and growth.

A handful of residents in Turpan interviewed by AFP on Thursday said they had heard about the incident but declined to elaborate.

Life went on as normal as residents napped on the side of the road near mud-brick homes and grape fields.

The reason for Wednesday's violence was not immediately clear.

A verified Twitter account by state-run broadcaster CCTV called the incident a "riot", saying it was correcting an earlier message which described it as an "insurgent attack".

According to official figures, 46 per cent of Xinjiang's population are Uighur, while another 39 per cent are Han Chinese, after millions from the majority group moved there in recent decades to find work.

The Han settlement drive has caused friction with the existing community.

Similar tensions have arisen in Tibet, which neighbours Xinjiang to the south.

Both are home to sizeable ethnic minority populations and are officially "autonomous regions" despite close oversight by Beijing.

Xinjiang saw its worst ethnic violence in years in July 2009 when riots involving Uighurs and Han settlers in Urumqi left around 200 people dead.

Chinese authorities closely restrict information about unrest in Xinjiang, blocking access across the region for several months after the violence in 2009.