Scores of workers from Foxconn, Apple's main manufacturer in China, have rioted after a dispute at a restaurant.
State media reported that the incident in Chengdu "was triggered by a conflict" between a group of workers and a restaurant owner.
Foxconn has been criticised for its treatment of workers, but officials said the dispute was not connected to working practices.
Foxconn produces products for Apple and Microsoft, among other companies.
The police said that the seven Foxconn workers were apparently annoyed by an argument between a restaurant owner and his wife on Monday.
The workers said the row had "affected their meal".
A fight broke out, and after the restaurant owner called the police, the workers ran back to their dormitory shouting: "They are beating us."
About 100 of their colleagues then joined the disturbance, throwing bottles, according to a statement published on the police's official microblog.
No-one was reported injured in the incident, but four workers were jailed for the night.
Hon Hai, Foxconn's parent company in Taiwan, told reporters that the seven workers who started the riot were new recruits.
The company said it was co-operating with the police investigation.
A string of suicides at Foxconn last year put the spotlight on working conditions at its factories.
Foxconn has since agreed to reduce hours, protect pay, and improve staff representation.