The protests began on 10 July in Kanmen in the coastal province of Zhejiang.
Workers - reportedly angered by a beating meted out to a colleague - attacked
a police station for three successive nights.
The incident comes just weeks after a 30,000-strong crowd torched dozens of
official buildings in Guizhou province.
They were protesting about an alleged cover-up over the death of a teenage
girl. Police said the girl committed suicide but her family said she was
murdered by the son of a local official.
One hundred people have been detained over the Guizhou riots, Chinese state
media reported on Monday, including "39 members of local gangs".
The incident in Kanmen erupted after a migrant worker was beaten by a
security guard, a Hong Kong-based human rights group said.
A crowd surrounded the police station after officers detained the worker, who
had gone to file a complaint, the Information Centre for Human Rights and
Three nights of protests and rioting followed, a local official website
"This was a grave crime of obstructing public security organs in carrying out
their duties and assembling a crowd to attack state offices," a local police
official was quoted as saying.
Three hundred military police arrived in the town on Sunday, another local
official told the Associated Press news agency.
In recent years, more and more reports of local protests have emerged from
Corruption, land seizures, abuse of power by local officials and the widening
gap between rich and poor are the common causes.
The incidents are of serious concern to Chinese authorities, who are keen to
present an image of social stability ahead of the Beijing Olympic Games.
Officials have been told to ensure local protests do not mar the Games.