A knife-wielding mob of suspected Islamic militants has rampaged through China's restive region of Xinjiang, killing dozens of people.

Many others were injured in the attack and Chinese police responded with gunfire, killing dozens of the militant group.

Chinese news agency Xinhua said dozens of militants were killed without giving precise figures.

"Initial investigation showed that it was a premeditated terror attack. Further investigation is under way," Xinhua said.

Chinese authorities in the region said they were not permitted to release any information about the attack.

It is notoriously difficult to find information from the region as officials restrict foreign journalist's access to the area.

The region has witnessed heightened violence this year from the minority Turkic Uighur Muslim group who believe that Beijing is clamping down on their religious freedoms.

In April, Chinese president Xi Jinping pushed the restive western region to the forefront of Beijing's counter-terrorism efforts.

"The situation is grim and complicated. The local-level police stations are fists and daggers," Xi told police.

"You must have the most effective means to deal with violent terrorists. Sweat more in peacetime to bleed less in wartime," he continued.

Last month, 81 people were found guilty of terrorism-related charges in the north-western region with nine being sentenced to death.

The sentences related to notable attacks such as a car ploughing into pedestrians in Tiananmen Square in October last year, killing five people, and a knife attack in April by a group of masked men killing 29 at Kunming train station.