Farmers storm police station in Yingde, Guangdong
The riot lasted more than four hours before being brought under control, but no information on damage or injuries was given.
Tea farmers in the city of Yingde have complained for years that authorities have not provided them with required medical insurance, social pensions and unemployment compensation, the China Daily reported.
Farmers protested twice this month, leading police on Friday to arrest four organisers suspected of planning larger demonstrations.
About 300 farmers gathered Saturday at the police station to demand the release of the four, but the rally became a riot when word spread that one of the men in custody had been killed.
Last year 87,000 incidents of social unrest were recorded by the Interior Ministry.
Workers denied wage and farmers deprived of their land without proper compensation often have no legal recourse to defend their rights. Thus they take to the streets and clash with police often used to protect the interests of business and local authorities.
Many incidents need very little to be set off.
Last week in Gansu more than a thousand protesters took to the streets, injuring 10 police and government officials and overturning police cars, media reported.
The riot was sparked by anger after officers allegedly beat a cyclist for running a red light.