Around 5,000 police were deployed to control a mass brawl among workers at a Foxconn plant in northern China, state media said Monday after the factory was closed for the day.

The electronics giant's vast plants in China churn out products for Apple and other tech firms, but it has been come under the spotlight after a series of suicides at its factories in the past two years.

Pictures posted online, the authenticity of which could not be confirmed, showed crowds of workers, a building with shattered windows, and an overturned police car, among other damage.

In a statement Foxconn's Taiwanese parent company Hon Hai said the incident began "as a personal dispute between several employees" in a privately-managed dormitory for workers at the plant in Taiyuan, in Shanxi province.

It escalated to involve 2,000 workers and was brought under control by police after four hours, the company said, adding 40 people were injured.

But China's state-run Xinhua news agency said a fight broke out between workers from two different Chinese provinces, "attracting more than 10,000 spectators and triggering chaos".

Around 5,000 policemen were sent to the scene, it said, citing government officials, and they needed 10 hours to bring the situation under control.

Foxconn is the world's largest maker of computer components and assembles products for Apple, Sony and Nokia, among others.

It employs about one million people 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.

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.

Numerous postings on the Sina Weibo microblog said the Taiyuan brawl was between factory security guards and workers.

"The facility was closed today, just today, in order for an investigation. It will be reopened tomorrow," Simon Hsing, spokesman for Foxconn's parent company Hon Hai told AFP.

The company statement added: "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."

A Taiyuan city government official said the unrest had "quietened down" and was not work-related. City police spokesmen could not immediately be reached for comment.

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.