Around 40 people have been injured in riots at one of Apple’s main suppliers. An estimated 1,000 to 2,000 people were involved in a mass brawl at the Foxconn plant in Taiyuan.

The incident began in a dormitory at the factory where staff lived. The company has been at the center of repeated allegations of poor labor standards and living conditions.

Foxconn says the disturbance began around 11pm local time last night. More than 5,000 police officers attended and regained control by9 am today. Production at the factory has been halted for the moment.

A government official has said early police investigations suggest it was sparked by a personal dispute between staff from different regions of China, while Foxconn says the incident wasn’t work-related.

However, unverified reports on social networks have put the blame on security guards violently attacking a worker in an earlier incident, with staff either rioting as a direct response or using the disturbance as an opportunity to seek revenge. Foxconn claims there was no property damage, though independent photos and videos show broken windows and a burned out van.

A spokesman for a Hong Kong group supporting Chinese labor rights suggested worker protests across the country are becoming more common, though only around five percent of such incidents lead to physical damage.

The Taiyuan factory is said to make some iPhone components, though isn’t the main production point for Apple in the country. Staff at the factory held a brief strike in March over pay and working conditions, reportedly because a promised pay increase didn’t materialize.