Workers at Foxconn’s Tiayuan plant in Northern China rioted Sunday evening, injuring 40 people and resulting in several arrests.

The riot was made up of about 2,000 people and took place outside of the workers’ dormitories. The cause of the riot is not certain, though The Next Web reports that Baidu posts claim the violence started when security guards began hitting a worker.

It is also unclear how much damage was done to the facility. The Next Web states that the Tiayuan facility is the same one infiltrated by an undercover journalist earlier this month to document the working conditions. That reporter worked on assembling parts for the iPhone 5 during his time there, meaning these riots could conceivably delay the shipment of more iPhone 5s.

This isn’t the first time Foxconn has seen a riot at one of its city-sized plants. In June of this year workers at Foxconn’s Chengdu plant rioted after workers accosted security guards in the worker dorms.

Foxconn is a Chinese manufacturer that is well-known for manufacturing Apple’s iPhones and iPhone parts. The company in the past has been criticized for its working conditions and for the multiple suicides committed by its workers. Foxconn has recently committed to cutting workers’ long hours and improving safety in their facilities.

Below is a video taken during the event, though the hectic nature of the footage and poor lighting make it nearly impossible to see what is happening. The second video appears to have been taken after the riot, and shows a bit of the aftermath, including the large police presence.