Employees at the world’s biggest iPhone factory were beaten and detained in protests over contract disputes amid anti-virus controls, according to witnesses and videos on social media on Wednesday, as tensions mount over Beijing’s severe coronavirus strategy.

Videos that said they were filmed at the factory in the central city of Zhengzhou showed thousands of people in masks facing rows of police in white protective suits with plastic riot shields.

The police kicked and hit a protester with clubs after he grabbed a metal pole that had been used to strike him. Frustration with restrictions in areas throughout China that have closed shops and offices and confined millions of people to their homes for weeks at a time with a little warning has boiled over into protests in some areas.

Videos on social media show residents in some areas tearing down barricades set up to enforce neighbourhood closures.

Last month, thousands of employees walked out of the iPhone factory operated by Taiwan’s Foxconn Technology Group over complaints about unsafe working conditions following virus cases in the facility.

A protest erupted on Tuesday over complaints Foxconn changed conditions for new workers who were attracted by offers of higher pay, according to Li Sanshan, an employee.

Li said he quit a catering job in response to advertising that promised 25,000 yuan ($3,500) for two months of work. Li, 28, said workers were angry after being told they had to work two additional months at lower pay to receive the 25,000 yuan.

“Foxconn released very tempting recruiting offers, and workers from all parts of the country came, only to find they were being made fools of,” Li said.

The ruling Communist Party promised this month to try to reduce disruption by shortening required quarantines and making other changes. But the party says it will stick to its “zero-Covid” strategy that aims to isolate every case at a time when other governments are relaxing travel and other restrictions and trying to live with the virus.