Beijing - China on Thursday said a string of unresolved "social grievances" and encouragement by criminal gangs sparked rioting by 30,000 people after the death of a teenage girl in the south-western province of Guizhou.

At a meeting on Wednesday, provincial leaders said local officials in Guizhou's Weng'an county had "failed to resolve disputes over mines, demolition of illegal buildings, immigration, reform of state-owned enterprises and many other issues", state media said.

"Some legitimate interests (of the people) were not effectively protected, and some people bore grievances," the Guizhou Daily newspaper said.

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.

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 police would mount a four-month crackdown on gangs and investigate the illegal possession of guns and explosives, gambling, and "other organized criminal activities," the agency quoted Luo as saying.

The Hong Kong-based Information Centre for Human Rights and Democracy said about 1,000 top Communist Party officials also met on Thursday in the provincial capital, Guiyang, to discuss the rioting.

The government said about 150 police and protesters were injured in the rioting, which began on Saturday night and continued for about seven hours.

The police had formally arrested 16 people after the rioters set fire to several government buildings and 42 vehicles, the agency 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.

The agency said people with no knowledge of the circumstances surrounding the girl's death were "incited to mob the buildings," forcing the police to use tear-gas and rubber bullets.

The riot was the latest 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. (dpa)