Eleven people were killed in an attack on a police station in China's restive Xinjiang, state media reported Sunday at a time of heightened tensions in the region following a fiery attack in Beijing.

Nine attackers and two auxiliary police officers were killed in the incident Saturday in Serikbuya township, near the historic Silk Road city of Kashgar, the official Xinhua new agency said, quoting local police.

Xinhua said the attackers were armed with knives and axes and that two other police officers were also injured. The agency gave no further details.

The cause of the violence, however, was disputed by a Xinjiang exile group, which claimed that Chinese security personnel opened fire on protesting Uighurs, the largest ethnic group in the vast western region.

Dilxat Raxit, a spokesman for the World Uyghur Congress, a Munich-based advocacy group, said a clash erupted after a Uighur youth was shot dead, with the eight others subsequently being killed.

"Several tens" of Uighur demonstrators were arrested, he said in an email citing what he described as locally provided information, while also mentioning the deaths and injuries of the four Chinese.

"I again call on international society to take emergency measures to stop the Chinese government from directly opening fire to suppress Uighur protesters and depriving them of using legal appeals and defending their rights," he said.

The bloodshed comes at a time of heightened tensions in the area where several violent incidents have occurred this year and following a fiery attack late last month in Beijing that the Chinese government blamed on terrorism.

The incident follows the deadly crash of a vehicle that erupted into flames at Beijing's Tiananmen Square last month. The government blamed the incident on "terrorists" from Xinjiang it said were backed by international Islamist militants.

The car, carrying three people from Xinjiang and also loaded with petrol canisters, drove into the gate of the Forbidden City on October 28. The incident left two dead besides the three people in the car, and 40 injured, according to Chinese police.

Beijing said separatists backed by the violent Islamist militant East Turkestan Islamic Movement were responsible.

Police called it a "carefully planned, organised and premeditated violent terrorist attack", adding that the vehicle also contained knives and banners bearing extremist religious content.

But that has largely failed to convince outside experts to accept the assertion of terrorism, citing the unsophisticated nature of the attack and the lack of an established Islamic extremist foothold in China.

Chinese state-run media have reported periodic bouts of violence in Xinjiang -- a huge, resource-rich region that makes up much of China's western flank -- which Beijing often describes as "terrorist attacks".

One such incident in June left 35 people dead, and 139 people have been arrested in recent months for spreading jihadist ideology.

The mainly Muslim Uighurs, the largest ethnic group in Xinjiang, routinely complain of rights abuses against them by the authorities and dismiss claims of terrorism and separatism as an excuse by Beijing to justify religious and security restrictions.

Information in the area is difficult to independently verify.