Authorities in the northern Chinese city of Taiyuan imposed a security clampdown in the streets around Taiwan's Foxconn Technology Group after the company halted production at its plant on Monday following riots involving around 2,000 workers.
"The plant is closed today for investigation," Foxconn spokesman Louis Woo told Reuters, but it was not immediately clear how long the shutdown would last at the factory, where 79,000 people are employed.
"They won't let anyone near the place," said an employee at a nearby factory in the provincial capital of Shanxi province. "It has all been sealed off since this morning; it seems they scaled up their response."
"I heard no one was going to work there today."
Around 5,000 policemen were dispatched to the scene of the disturbance, which began as a dispute between workers of different age groups in a dormitory building, and raged until 9:00 a.m. Monday morning, official media reported.
Police and company officials are still investigating the cause of the disturbance, but the official Xinhua news agency said it was sparked by a fight between rival groups of workers who banded together out of loyalty to those from their hometowns.
Forty people were sent to the hospital after the incident, three of whom remained in a "serious condition" following the riot, Xinhua news agency reported, citing Taiyuan government officials.
"The fight started at 11:00 p.m. in the site's dormitory zone in Taiyuan, attracting more than 10,000 spectators and triggering chaos," the agency quoted a police statement as saying.
It said government officials had denied media reports that there had been a halt in production, however.
String of suicides
The unrest at Foxconn, which assembles Apple's iPhone 5 and is the world's largest contract maker of electronic goods, came after a series of labor incidents at the company's factories, including a string of worker suicides last year.
The company has been slammed for poor working conditions and mistreatment of employees at its China facilities, and says it has spent heavily in recent months to improve conditions and to raise wages.
In a statement on Monday, Foxconn said the incident escalated from "a personal dispute between several employees" late on Sunday.
"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.
Online comments blamed the factory's own security guards, however.
User @jo-liang said on China's popular Sina Weibo microblogging service that four or five security guards beat a worker almost to death. And according to @fandesahai, guards beat up two workers from Henan province, which incited workers to set fire to company property in retaliation.
According to Geoff Crothall, communications director at China Labour Bulletin, the incident was testament to the "deep-seated frustration and anger among [Foxconn] employees and no outlet, apart from violence, for that frustration to be released."
"There is no dialogue and no means of resolving disputes, no matter how minor. So it is not surprising when such disputes escalate into violence," Crothall told Reuters in a statement.
Reported by Fang Yuan for RFA's Mandarin service. Translated and written in English by Luisetta Mudie.