Up to 50,000 workers, upset over alleged mistreatment by local security forces, clashed with police in a town in China's Guangdong province.
The riot took place Saturday in Da Lang village in Guangdong province, after police allegedly beat to death a relative of a student injured in a traffic accident following a dispute over compensation.
The rioters threw rocks and bricks and set fire to four police cars before police brought the violence under control.
There were unconfirmed reports that some people were killed when police fired into the crowd.
Authorities in Dongguan county and in Dalang township declined to comment.
The unrest was the latest in a string of riots and clashes in rural China that have highlighted discontent over rampant government corruption and abuse of power.