Beijing - China has placed in criminal detention 100 people charged with offences linked to rioting last month in the south-western province of Guizhou, including 39 members of local gangs, state media said on Monday.

The 100 detainees were among 355 people identified by police as suspected of committing criminal offences during rioting by up to 30,000 people prompted by the death of a teenage girl in Weng'an county, the official Guizhou Daily reported on its website.

Police identified some 90 gang members who joined the rioting and urged those not in custody to give themselves up, the newspaper said.

The government earlier said a string of unresolved "social grievances" and encouragement by criminal gangs sparked the rioting on June 28, when rioters set fire to several government buildings and 42 vehicles.

About 150 police and protesters were injured in the rioting, and the police used tear-gas and rubber bullets, reports said.

Many rioters believed that local authorities had covered up the rape and murder of the 17-year-old girl because the chief suspect was the son of a top county official.

But police said the girl died after committing suicide by jumping into a river.

They said they found no link between her and relatives of local officials, and that three autopsies found no evidence of rape or murder.

But provincial leaders said some locals "bore grievances" because officials had "failed to resolve disputes over mines, demolition of illegal buildings, immigration, reform of state-owned enterprises and many other issues," the newspaper reported earlier.

Officials said that about half of the estimated 600 to 800 crimes committed annually in Weng'an remained unsolved.

Theft, robbery and assault were "frequent occurrences," the official Xinhua news agency said, adding that several officials faced disciplinary investigation.

Luo Yi, the police chief of Qian'nan prefecture, which administers Weng'an, said the violence was "fanned and exacerbated by local gangs and criminals, who were organized in sending gasoline, machetes, clubs and fireworks to aid the destruction."

The riot was one of an increasing number of protests and violent incidents in recent years, reflecting simmering unrest over abuse of official powers and widespread cynicism towards the ruling Communist Party in many poor areas.

The Hong Kong-based Information Centre for Human Rights and Democracy said hundreds of migrant workers rioted last week in the eastern province of Zhejiang, following alleged mistreatment of a colleague.

Some 300 paramilitary police sent to quell the rioting had arrested about 30 workers after the rioters surrounded a police station and smashed vehicles, the group said. (dpa)