Uncertainty was still stalking the streets of Urumqi, in western China, Friday morning despite heavy security and patrolling helicopters in the sky in the wake of a wave of hypodermic needle stabbings and massive protests.

Helicopters were seen hovering over the city Friday morning, the second time here since the July 5 riot that left 197 people dead.

"I bought a lot of food today. Who knows what will happen next," said Luo Huanzhang, who just returned from a regular morning outdoor market on the Guangming Road.

The market was crowded and many people intended to stock up groceries, Luo said. Residents also keep their forays into public places short.

"I don't know whether I should go to work," said an employee with the Xinjiang branch of China Life Insurance (Group) Company, who only offered his surname of Tang.

Traffic controls imposed at 9 p.m. Thursday banned vehicles on major roads in downtown areas such as Youhao Road, Guangming Road and Renmin Square.

People have to walk or cycle, but many chose to stay at home.

Bedclothes seller Chen, 28, said she closed her shop on Wednesday as protests against the needle attacks?flared up.

"People were so upset and unnerved recently. Doing business was almost impossible," said Chen.

"My friends kept asking me to return to my hometown and I'm still thinking about it," said Chen, who has lived in the city for 26 years since arriving with her parents from Chongqing, in southwest China.

"My career is rooted here, I don't want to leave," said Zhang Shiying, who runs a construction material shop in the city's northern area.

Zhang, a native of Beijing, opened his business in Urumqi 14 years ago.

The Experimental Primary School of Urumqi was closed Friday and it was unclear when it would resume classes on Monday, said a teacher who declined to be named.

Police in the capital of Xinjiang Uygur Autonomous Region have detained 21 people, of whom six are in police custody and four have been referred for criminal prosecution, said the regional information office in a mobile phone text message to the public on Thursday.

It also said the courts would hand down severe punishments to those found guilty.

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 requested the procuratorate to approve the arrests of another 239 suspects thought to be involved in 140 crimes. Another 825 are being held in criminal detention, the regional information office said.

The press office of the regional government sent cell phone text messages to people Friday, saying the city had registered 476 people who had sought treatment for needle stabbings, of whom 89 were showing obvious signs of needle wounds. They comprised members of nine ethnic groups, including Hans and Uygurs.

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

(Xinhua News Agency September 4, 2009)