Production had to be suspended after a personal dispute triggered a mass brawl late on Sunday night, involving up to two thousand workers, who make parts for the new iPhone 5.
Please wait while this video loads. If it doesn't load after a few seconds you may need to have Adobe Flash installed.
As workplace brawls go, this one was as big as it gets. According to one worker in Taiyuan, unrest broke out after security guards bullied a staff member, prompting his colleagues to rally round. They apparently rounded on the guards, who were all from a different province, and the dispute flared.
Another worker, contacted by Sina Corp's microblogging service, said motorbikes had been set on fire and store windows smashed. Photographs posted on the internet show a crowd of at least a thousand milling around.
According to police, the dispute was finally brought under control at around 3am on Monday morning. Foxconn said that forty people had been taken to hospital, while "a number of individuals were arrested."
An investigation is being carried out into what happened, as company spokesman Louis Woo said production was being suspended: "Our decision is to take a day off for that particular plant today."
The plant is part of Apple's new i-Phone 5 supply chain, making parts for the casing, although supplies of the phone itself are not thought to have been disrupted by last night's incident.
Foxconn, which is part of Hon Hai Precision Industry, is the world's biggest manufacturer of consumer electronics: as well as the i-Phone and i-Pad, its far eastern workers also make the Amazon Kindle and the market's top selling smart phones.
Founded in 1974, its Chinese workforce is almost a million strong. The Taiyuan plant alone employs around 79,000 people: according to the Chinese publication China Story, staff there were told they should feel "honour" for producing parts for the i-Phone 5.
Demand for the new phone has pushed share prices up sharply this year, although Foxconn continues to be the subject of allegations about bad working practices and poor conditions.
The company says it has now taken steps to improve conditions, after the negative publicity surrounding a spate of suicides in its massive Shenzen operation in 2009 and 2010.
Under the factory town model, hundreds of thousands of workers were housed in dormitories next to the plant, sharing rooms with six strangers, working long hours and six day weeks.
Since an outside audit found "significant issues", Foxconn raised wages, shortened the work week, and brought in psychological counsellors to help its workforce, especially the teenage migrant workers who struggled to cope with boredom and loneliness.
According to the Wall Street Journal, the new generation of workers are more demanding than their elders, resulting in better wages and benefits. However, earlier this month reports claimed students were being forced to work on production lines as part of compulsory internships.
The company has defended its conduct, while there has been no comment from Apple. But as last night's brawl has starkly revealed, tensions among the vast workforce are still perilously close to the surface.