Chinese state media say hundreds of people have attacked police and smashed their cars in the capital of southwestern China's Guizhou province.
The Guizhou Metropolitan newspaper says Monday's riot began in Guiyang city after police officers allegedly beat a migrant who had refused to pay for a temporary residence permit.
One police officer and a taxi driver were injured in the clash. At least four people were arrested.
Social unrest is becoming more common in China.
Last month, university students in central China smashed windows and ransacked their campus, angered by a disagreement with the university administration.
Other episodes of public violence have been linked to the country's increasing gap between rich and poor and to outrage over land seizures and allegations of corruption in government.