FORTUNE — The footage posted late Sunday local time on China’s YouKu video hosting service (and picked up on YouTube) shows a scene that will be familiar to anyone who lived through the student protests of the 1960s: Crowds of young people gravitating toward the center of the action. Excited laughter and giggling punctuated by angry shouts, screams and finally what sound like gunshots.

The authenticity of the 4:44 minute video has not been officially confirmed, however. Nor does it shed light on what triggered the riot at Foxconn’s (FXCNY) Taiyuan plant in northern China or what exactly was being made there.

A Chinese newspaper’s undercover investigation in August reported that the plant, which employs nearly 80,000 workers, was involved in making parts for Apple’s (AAPL) iPhone 5. But an analyst quoted by Bloomberg said that Apple had “little manufacturing exposure” at the factory, and that it was more likely producing other devices such as Nintendo’s (NYDOY) Wii.

Also unclear is what caused the riot in the first place. Early reports on Chinese social media sites monitored by Engadget‘s Richard Lai said the disturbance began when a security guard struck a worker and grew into a brawl that hospitalized 40 and led to up to 20 arrests.

A spokesman for Foxconn, who initially put the number injured at 10, said it started as a dormitory fight between two competing work groups.

Photos posted on Chinese sites show broken shop windows and an overturned guard station. Eventually paramilitary and other police were called in to restore order. Foxconn announced Monday that the plant would be closed while the incident is being investigated, but that it will reopen Tuesday.

A spokesman for the China Labor Bulletin, a nonprofit advocacy group in Hong Kong, told the
New York Times
that workers on the mainland have become increasingly emboldened. “They’re more willing to stand up for their rights, to stand up to injustice,” he said.