Uighur residents gather near a barricade set up to fend off a possible Han Chinese attack in Urumqi on Wednesday. (Ng Han Guan/Associated Press)

Thousands of paramilitary police took to the streets in the capital of China's Xinjiang province on Wednesday, as government officials vowed to severely punish those involved in the deaths at the massive protests that have occurred in recent days.

Paramilitary police guarded the roads around Uighur neighbourhoods in Urumqi as helicopters dropped leaflets onto the city continuing to appeal for calm.

"[Communist Party] Secretary Wang [Lequan] urges everybody to return home, return to their work units and return to their communities," said the leaflet.

At least 156 people have died in ethnic violence between Han Chinese and minority Muslim Uighurs in the northwestern province of Xinjiang since Sunday.

Chinese paramilitary police patrol in Urumqi, western China's Xinjiang province, on Wednesday. (Eugene Hoshiko/Associated Press)

Urumqi Communist Party chief Li Zhi told reporters Wednesday the death penalty will be sought for anyone found to be behind the riot's killings.

Zhi said both ethnic groups were responsible for the violence and many of those accused of the killings have already been detained. Several of the arrested rioters are students, he said.

"To those who committed crimes with cruel means, we will execute them," he said, adding government forces will crack down on any further security risks.

Officials said that there were only scattered clashes on Wednesday but there were also media reports that police were in a standoff with about 1,000 Han Chinese near a bank.

"The government told us today not to get involved in any kind of violence. They've been broadcasting this on the radio and they even drove through neighbourhoods with speakers telling people not to carry weapons," a Han Chinese man, who asked to go unnamed, told The Associated Press.

Though a curfew on Tuesday night had cleared people off the streets, there were reports that neighbours began attacking each other near their homes.

Video and photographs shown to reporters by Uighur residents showed Han Chinese mobs armed with sticks storming neighbourhoods and blood stains on streets and building walls.

"They came in here and struck people with sticks and threw rocks at us. They were carrying the Chinese flag. I never imagined that something like this could happen," said a university student only identified as Parizat told The Associated Press.

Internet access blocked

Authorities continued to try to control the unrest on Wednesday by blocking internet social networking sites and limiting access to text messaging services and mobile phones in the region.

Internet cafes in Turpan and Kashgar said they had been ordered to shut down by police for three days.

Chinese President Hu Jintao has left the G8 summit in Italy to return to Beijing amid the outbreak of violence.

The Uighurs, an ethnically Turkic, predominantly Muslim group make up the majority in Xinjiang, a region in northwest China bordering Central Asia and Mongolia.

Their relations have often been tense, with the ethnic Han Chinese who predominate in the country. Many Uighurs feel they're discriminated against by the government in Beijing and a Uighur separatist movement has existed for decades.

Many Uighurs believe the Han Chinese, who have flooded into the rugged, rapidly developing western region in recent years, are trying to crowd them out. The Han Chinese say the Uighurs are backward and ungrateful for all the economic development and modernization.

The protests started in the provincial capital of Urumqi on Sunday, when demonstrators gathered to demand justice for two Uighurs killed in June during a fight with their Han co-workers at a factory in southern China.

The protests turned into the deadliest ethnic unrest in the region in decades. Officials have said that more than 1,000 have been injured and that about 1,400 have been detained.

Hundreds of vehicles, stores and street vendor stalls were also damaged or set ablaze during the protests, officials said.

With files from The Associated Press