Beijing - Riot police beat and detained protestors in southern China's Guangdong province after more than 500 people blocked a main road because of a dispute with local officials, residents and a US-based rights group said on Thursday.

"The farmers who were the leaders of the protest were arrested by the police," one local resident told Deutsche Presse-Agentur dpa by telephone from Guangdong's Sanjiang township.

Another local resident said Sanjiang was "quiet" on Thursday, following the riot on Wednesday.

US-based Human Rights in China quoted witnesses as saying more than 500 people joined the protest and that police used batons to disperse the crowd, "leaving some seriously injured and unconscious."

The police also detained several residents who recorded the incident on their mobile telephones, the group said.

The sit-in was staged to protest local officials' management of the area near a dam that collapsed during a recent typhoon in Sanjiang's Shenlei village, it said.

Flooding from the dam-burst destroyed crops, fish ponds and other property, with villagers blaming the disaster on the officials' decision to remove protective palm trees near the dam a few months ago.

Farmers were also angered by the refusal of the local government to compensate them for losses suffered after the collapse of the dam, the group said.

The incident is the latest sign of growing unrest and violence in rural areas, where many residents accuse local officials of corruption and abuse of power. (dpa)