The Taiyuan plant, which employs about 79,000 workers, makes automobile electronic components, consumer electronic components and precision moldings. An employee told Reuters the plant also makes parts and assembles Apple's iPhone 5.

In a statement, Foxconn cited police as saying about 40 people were taken to hospital for medical attention and a number were arrested.

The company said the incident escalated from what it called a personal dispute between several employees at around 11 p.m. on Sunday in a privately managed dormitory, and was brought under control by local police at around 3 a.m.

"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," Foxconn said.

China's Xinhua News Agency, citing Taiyuan City's public security bureau, reported that about 10 people were hurt in the fighting and around 5,000 police were sent to the scene, bringing it under control as of 9 a.m.

"The plant is closed today for investigation," said Foxconn spokesman Louis Woo.

Foxconn, the trading name of Hon Hai Precision Industry Co and the world's largest contract maker of electronic goods, has seen a few violent disputes at its sprawling plants in China, where it employs a total of about 1 million workers.

By late morning, Hon Hai shares were down 1.03 percent, lagging the broader market's rise of 0.1 percent.

In June, about 100 workers went on a rampage at a Chengdu plant in southwestern China. The company has faced allegations of poor conditions and mistreatment of workers at its China operations, and has been spending heavily in recent months to improve the work environment and to raise wages.

A staff member at the Taiyuan plant said he was told the plant could be closed up to two to three days for police investigations.

"There are a lot of police at the site now," the staff member, who asked not to be named because he is not authorized to speak to media, told Reuters by telephone.

Calls to the Taiyuan police were not immediately answered, while an official at the plant declined to comment when reached by telephone.

(Additional reporting by Sally Huang and Ben Blanchard in Beijing; Editing by Jonathan Standing and Ken Wills)

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