Authorities in Urumqi, capital of northwest China's Xinjiang Uygur Autonomous Region, had sent more than 20,000 armed police, special police, firefighters and troops to quell Sunday's unrest, a source with the city's police department said Monday.

The unrest has led to the deaths of at least 140 people, and injured another 828 as of Monday. The death toll could still be rising.

The police and soldiers used tear gas grenades, stun grenades, and high-pressure water guns, the source said.

According to the police source, the police department of Urumqi was tipped off in the early hours of Sunday that information was spreading on Internet forums, calling for demonstrations at the People's Square and South Gate at 7 p.m. Sunday.

About 2,000 police officers were then deployed at the People's Square and the Erdaoqiao Street about one kilometer away.

By 7 p.m., several hundred people had gathered at the People's Square. Violence began around 8 p.m., when some rioters started beating pedestrians and smashing buses. The violence soon spread to many other downtown areas.

The regional police department sent armed police and special police forces to disperse and arrest the rioters, the source said.

By Sunday midnight, more than 20,000 armed police, special police, firefighters and troops were sent out to quell the unrest.

Several hundred people, including at least a dozen who were suspected of fanning the unrest, had been arrested by the police, Liu Yaohua, the region's police chief, said Monday.

(Xinhua News Agency July 7, 2009)