Police in Southwest China's Guizhou Province have busted five criminal gangs involved in a riot in Weng'an county in 2008 and arrested 15 local officials who allegedly "provided protection" to the outfits, a top official said on Friday.

A total of 240 gangsters have so far received sentences up to life behind bars for inciting or being involved in the riot, which left more than 150 people injured, Cui Yadong, director of the Guizhou provincial public security department and deputy to the National People's Congress (NPC), said on the sidelines of the annual session last week in Beijing.

"The key reason behind the riot was instigation from gangsters," Cui told China Daily.

However, he also admitted that "negligence and the mishandling of public sentiment" on the part of the local government fueled the riot. "The gangsters would not have succeeded otherwise."

"The local governments face immense pressure to handle rising disputes," he said.

The Weng'an riot on June 28, 2008 shocked the nation, as more than 30,000 people poured onto the streets, smashing government buildings and torching police vehicles, in protest at the death of 15-year-old Li Shufen.

Initial police investigations found the schoolgirl drowned. However, Li's family, who claimed she was raped and murdered, demanded compensation from the government.

More than 150 police officials and protesters were injured in the violent protest that broke out. About 160 offices and more than 40 vehicles were also set ablaze.

Three autopsies were later conducted on the girl's body, which concluded she died due to drowning.

Cui said that following the riot, police launched a crackdown on gangsters and officials who protect them. So far, 15 officials have been arrested, he added.

He said one of the key tasks for Guizhou police this year is to continue fighting groups of organized crimes and their "protection umbrellas".

"From my experience, where there's a mafia-style gang, there must be some officials who are hand-in-glove with them," Cui said. "To an extent, fighting those corrupt officials is more important than seizing a few gangsters."

According to Cui, prevention is the best way to fight gang-related crimes.

He said groups of organized crimes are actually very easy to bust, as their development takes time. "It's a growing process. There's no way our police officers have no idea about the gangs."