At least 12 people have died in riots in Yecheng county, near the city of Kashgar in China's restive north-western Xinjiang province, China's state media has reported.
Rioters armed with knives allegedly attacked victims in Yecheng around 6pm local time on Tuesday evening. Ten people were killed by rioters, and police shot two of the attackers dead, according to China's Xinhua news agency. Police are looking for suspects. The brief report did not say what triggered the attacks, or give any further details about the rioters.
Xinjiang is home to China's Uighur ethnic minority, who make up 41.5% of the region's 21 million people and speak a Turkic language, very different from Mandarin. The county has seen persistent outbreaks of unrest, and has a heavy security presence.
Police and government officials in Yecheng, Kashgar and Urumqi, the regional capital of Xinjiang, were not answering calls.
Censors have begun blocking internet searches for Yecheng and Kashgar. Searches for both Yecheng county and Kashgar on the news service Sina's Weibo microblog brought only a message saying results could not be shown due to regulations.
Microbloggers have often been quick to spread eye-witness accounts of disasters, accidents and other politically-sensitive events.
Almost 200 people died, mostly thought to be from China's majority Han Chinese ethnic group, and 1,700 were injured when riots erupted in Urumqi in July 2009. Fighting broke out between Uighurs and migrant Han workers and buses were overturned and set on fire. Vicious assaults on Han were followed by revenge attacks on Uighurs.
Since then, Chinese authorities have stepped up already tight security in Xinjiang. In January, authorities announced a police recruitment drive that will add 8,000 extra officers, allowing one police officer in each village. Part of their duties will be to crack down on illegal religious activities, as well as security patrols and dealing with migrant workers.
A senior government official said: "It is an important move for Xinjiang to consolidate the foundation of security and ensure lasting peace and stability in the region."
China's border regions are increasingly seeing ethnic unrest. Riots in the Tibetan capital, Lhasa, led to 23 deaths in March 2008, the Chinese government has said, but Tibetan exile groups say more people died in the ensuing crackdown. Over the past 12 months, Tibetan areas of western Sichuan province have seen rioting and self-immolation protests by monks and nuns.
Mongolian students also took to the streets in 2011 after a herder was killed after being run over by a coal truck. They protested against extensive mining operations on traditional grazing land.
Southern Xinjiang saw three outbreaks of violence in July 2011, according to state media. A group of Uighurs was said to have stormed a police station in Hotan, taking hostages and killing four. On 30 and 31 July, another Uighur group in Kashgar hijacked a truck, set a restaurant on fire and stabbed people in the street, state media reported. Chinese authorities say police shot 14 attackers in Hotan and five in Kashgar, but exile groups have disputed those accounts.
China says terrorist groups are behind violence in Uighur areas, while exiled Uighur groups blame Chinese repression and unequal economic opportunities.