Security forces in far-west China's strife-hit city of Urumqi used tear gas to break up fresh protests on Friday, as thousands of Han Chinese demanded better security after a scare over claimed attacks with syringes.

The protesters massed in the streets in Urumqi, capital of the Xinjiang region, for a second day to protest that authorities were too slow to punish Uighurs behind deadly riots on July 5.

The Han also said they were the targets of mysterious attacks with syringes.

"Tear gas has been deployed to disperse the protesters," the official Xinhua news agency said in a brief English-language report.

Earlier, police vans patrolled the streets with loudspeakers, telling people to go home and maintain order. But with schools closed and bus routes through the city interrupted by road blocks, most in the crowds had little to do but mill about.

Schools were shut on Friday after students helped spearhead Thursday's noisy protest, when crowds called for regional Party Secretary Wang Lequan to resign.

Panic has risen in the city since government text messages a week ago warned of attacks with syringes. Some parents were afraid to send their children alone to classes when schools were open earlier in the week.

"They have no right to block off the road like this. These Uighurs have been stabbing us with needles," said a man trying to push through barriers sealing off a Uighur neighbourhood.

"We need to take care of the problem."     Paramilitary troops and police manoeuvred around the city to diffuse the angry crowds gathered at intersections.

Many in the crowd tried to argue directly with police, calling for "more rights for Han people".

A group of young Han Chinese men unfurled a Chinese flag and tried to lead a march to People's Square, followed by several hundred people shouting "safety". Police snatched away the flag, but the crowd continued shouting.

"The main thing is nobody here feels secure any more," said onlooker Zhen Guibin. Many people complained that those behind the killings on July 5 had not been tried.

A July 5 protest by Uighurs, a Turkic-speaking Muslim people native to the area, gave way to a spree of violence across the city in which 197 people were killed, most of them Han Chinese. Two days later, Uighur neighbourhoods were attacked by Han Chinese demanding revenge.

"Terrorist crime"

Li Zhi, Urumqi's Communist Party boss, raised the political stakes on Thursday by saying the syringe stabbings were part of a plot by separatist forces to sow conflict, the official Xinhua news agency said.

"This was a grave terrorist crime," Li said in a speech.

"The goal was to create ethnic division and stir up ethnic antagonism in a bid to overturn social order, split the motherland and split the Chinese nation."

China says Uighurs campaigning for independence are allied with Islamist militants in the region, and there have been occasional deadly bomb attacks on government targets in Xinjiang.

Xinjiang's population is divided mainly between Uighurs, long the region's majority group, and Han Chinese, many of whom moved there in recent decades. Most Urumqi residents are Han.

The Xinjiang government, apparently trying to staunch anger, announced on Thursday that 196 suspects have been charged over the July riot. Fifty-one were indicted and will face prosecution.

The government announced the indictments via text messages to Urumqi residents from Wednesday evening, after a small protest that day over the syringe attack reports. The announcement was reported by Xinhua news agency late on Thursday.

Some Han Chinese residents were unimpressed.

"I think the government has been way too lax towards the Uighurs," said a Han shop owner who identified himself as Zhang.

"This policy has got to change. We shouldn't have all these minorities