TAIYUAN, China (CBS) -- Security was tight on Monday evening around Taiwan's Foxconn Technology Group factory which assembles Apple's iPhones in northern China after about 2,000 workers were involved in a brawl at a company dormitory.

Police vans guarded the main gates of the plant, while over 100 paramilitary police officers could be seen inside the complex near a gate where windows of the security office had been smashed.

At least two other gates had been attacked, leaving shards of glass on the ground and buckled railings.

Foxconn Technology Group, which also makes components for top global electronics companies, closed the plant in Taiyuan, capital of Shanxi province, on Monday after the brawl late on Sunday (September 23) night.

It was not clear how long the shutdown would last at the plant, which employs about 79,000 people, while police and company officials investigate the cause of the disturbance.

Foxconn said the trouble started with a personal row that blew up into a brawl.

But some people said they had heard factory guards had beaten workers, sparking the melee.

The accounts could not be independently confirmed on Monday.

The unrest is the latest in a string of incidents at plants run by Foxconn, the trading name of Hon Hai Precision Industry Co and the world's largest contract maker of electronic goods. A supplier and assembler for Apple products, the company has faced accusations of poor conditions and mistreatment of workers at its operations in China, where it employs about 1 million workers.

The company has been spending heavily in recent months to improve working conditions and to raise wages.

The state-run Xinhua news agency reported that about 5,000 police were sent to end the violence, according to Taiyuan City's public security bureau.

Foxconn cited police as saying 40 people were taken to hospital and a number were arrested, while Xinhua added that three people were in serious condition.