The city of Urumqi, capital of northwest China's Xinjiang Uygur Autonomous Region, quieted down late Thursday night after tens of thousands of people took to streets to protest against syringe attacks.

There were few pedestrians on the Youhao, Karamay, Altay and Beijing Roads. Police were persuading about 100 people to leave the Nanhu Square in front of the municipal government.

Li Zhi, secretary of the CPC Urumqi City Committee, calls on the crowds yesterday to stay calm and show restraint. [Xinhua]

Passage in areas including Youhao Road, Guangming Road and Renmin Square was prohibited for vehicle as a traffic control in place on major roads in downtown areas took effect at 9:00 p.m..

The daytime protest, attended by tens of thousands of people, crippled city traffic and forced shops in major commercial streets to shut.

Police said Thursday's protest started at 10:50 a.m. when more than 1,000 people gathered in the residential quarter of Xiaoximen. Another crowd of protestors gathered at the Beiyuanchun farmers' produce wholesale market at 10:30 when a man was caught after allegedly stabbing a five-year-old girl.

The demonstration spread to major streets including Guangming Road, Xinmin Road and Youhao Road. People also turned out in big crowds in front of the Renmin Cinema and at the Renmin Square.

Protestors held the national flag and the flag of the Communist Party of China and shouted "Severely punish the mob." Members of the Uygur ethnic minority were among the protesting crowds.

Wang Lequan, secretary of Xinjiang Uygur Autonomous Regional Committee of the Communist Party of China (CPC), and Li Zhi, secretary of the CPC Urumqi City Committee, called on the crowds, on two separate occasions, to stay calm and show restraint.

Wang and five representatives of the public held talks in the office building of the regional committee during the afternoon, but no details were available.

Stabbing attacks occurred during the protests and an attacker was caught at the scene. The police stopped the crowd who were about to beat her.

Police said that attacks with syringes against innocent people have been carried out in Urumqi since Aug. 17. The regional health department said 476 people have sought treatment for stabbing, of whom 89 were showing obvious signs of needle sites.

As of Wednesday, there had been no deaths reported and no symptoms have been found of infectious disease viruses or toxic chemicals.

Parents are worried about the safety of their children as the Fall semester has started.

Zhu Hailun, head of the political and legal affairs commission of the CPC committee in Xinjiang, said members of nine ethnic groups including Han, Uygur, Hui, Kazak and Mongolian had reported stabbing incidents to the police in recent days.

Local police had seized 21 suspects, of whom six are in police custody and four arrested for criminal prosecution, said the regional information office in a mobile phone text messages to the public on Thursday.

It also said that the court would hand down severe punishments to those found guilty according to the law.

The attacks came less than two months after the July 5 Urumqi riot when 197 people, mostly from the Han ethnic group, were killed, and 1,600 others injured.

Authorities have issued arrest warrants to 196 suspects and prosecuted 51 for involvement in the riot, the regional government information office said in a statement Thursday. The police have further requested the procuratorate to approve the arrest of another 239 suspects thought to be involved in 140 crimes. Another 825 are being held in criminal detention, the regional information office said.