Electronics giant Foxconn, whose vast plants in China churn out products for Apple and other tech firms, shut a factory Monday after a brawl involving some 2,000 workers, officials said.
Around 40 people were injured in the incident in Taiyuan in northern China, which began around 11:00 pm Sunday and was not brought under control by police until four hours later, Foxconn's parent company Hon Hai said.
Pictures posted online, which could not be confirmed, showed crowds of workers, a building with shattered windows, and an overturned police car, among other damage.
"The facility was closed today, just today, in order for an investigation. It will be reopened tomorrow," Hon Hai spokesman Simon Hsing told AFP.
Foxconn is the world's largest maker of computer components and assembles products for Apple, Sony and Nokia, among others. The company has come under the spotlight after suicides and labour unrest at its Chinese plants in the past two years.
The company statement said the trouble began "as a personal dispute between several employees" in a privately-managed dormitory for workers at the plant in Shanxi province.
"The cause of this dispute is under investigation by local authorities and we are working closely with them in this process, but it appears not to have been work-related," it said.
Numerous postings on the Sina Weibo microblog, which could not be confirmed by AFP, said the brawl was between factory security guards and workers.
In 2010, at least 13 Foxconn employees in China died in apparent suicides, which activists blamed on tough working conditions, prompting calls for better treatment of staff.
"Foxconn is known to have a very authoritarian management style and discipline is very strict," Geoffrey Crothall, spokesman of the Hong Kong-based China Labour Bulletin, told AFP.
"When you have a working environment like Foxconn where workers are treated simply as units of production, essentially robots, not human beings... then sometimes violence is the only way out (and) you see minor disputes escalating into violence."
Following the spate of suicides, Foxconn rolled out a series of measures, including wage hikes and safety nets outside buildings, and has since been expanding its workforce throughout China.
In January, workers at a Foxconn plant in Wuhan, in central China, that makes Xbox game consoles for computer giant Microsoft "staged a workplace incident" over a plan to transfer staff, Foxconn said at the time.
About 45 workers resigned afterwards, the company added, offering few details.
Foxconn employs about one million workers in China, roughly half of them based in its main facility in Shenzhen, which borders Hong Kong.
The Taiyuan plant employs 79,000 workers and makes automobile electronic components, consumer electronic components and precision mouldings.
A Taiyuan city government official said the unrest had "quieted down" and was not work-related. City police spokesmen could not immediately be reached for comment.