Tens of thousands of people protested in the capital city of China’s far-west Xinjiang region on Thursday to demand security guarantee from authorities, according to the Xinhua news agency.

The protest in Urumqi began in the morning over claims that residents had been attacked with syringes and “more than 1,000 people started to gather”, a police officer told Xinhua. The report did not identify the officer.

The report said protesters gathered in a neighborhood called Xiaoximen, and there were also gatherings at the Renmin Cinema and Beiyuanchun farmers' produce wholesale market.

An overnight curfew was declared throughout the city. 

“Resign Wang Lequan, the government is useless!” protesters shouted outside the regional government building in Urumqi, referring to Xinjiang’s Party chief, who has held office for 14 years. Others called for his execution.

Eyewitnesses say Wang tried to give a speech in central Urumqi's People's Square in the afternoon, but his speech was cut short by protesters who threw plastic water bottles at him.

Protesters demanded police protect them from the spate of syringe stabbings that had taken place in the city since Aug 3.

Xinhua said 21 people were detained and four arrested in connection with the attacks, but did not say what ethnic group they belonged to.

Local authorities did not acknowledge the stabbings until Wednesday afternoon, after several hundred ethnic Han residents took to the streets, demanding safety.

The protesters on Thursday also called on the government to severely punish the offenders of the new violence and the killings on July 5.

The July 5 riot left at least 197 people, mostly Han residents, killed and more than 1,700 injured, according to official statistics. Inside sources, however, claimed the actual deaths were around 400.

Ethnic Han residents first protested against the July 5 violence, the most brutal in decades, and called for immediate government protection two days later when they clashed with Uygurs throughout the city, triggering a curfew.

Li Zhi, Party boss of Urumqi, speaks to crowds in this capital city of Xinjiang Uygur Autonomous Region, Sep 3, 2009.