SHANGHAI/TAIPEI: Hundreds of workers joined protests at Foxconn's flagship iPhone plant in China, with some men smashing surveillance cameras and windows, footage uploaded on social media showed.

The rare scenes of open dissent in China mark an escalation of unrest at the massive factory in Zhengzhou city that has come to symbolise a dangerous build-up in frustration with the country's ultra-harsh COVID rules as well as inept handling of the situation by the world's largest contract manufacturer.

The trigger for the protests, which began early on Wednesday, appeared to be a plan to delay bonus payments, many of the demonstrators said on livestream feeds. The videos could not be immediately verified by Reuters.

"Give us our pay!", chanted workers who were surrounded by people in full hazmat suits, some carrying batons, according to footage from one video. Other footage showed tear gas being deployed and workers taking down quarantine barriers.

Discontent over strict quarantine rules, the company's inability to stamp out outbreaks and poor conditions including shortages of food has caused workers to flee the factory campus since the Apple Inc supplier imposed a so-called closed loop system at the world's biggest iPhone plant in late October.

Under closed-loop operations, staff live and work on-site isolated from the wider world.

Former workers have estimated that thousands fled the factory campus. Before the unrest, the Zhengzhou plant employed some 200,000 people. To retain staff and lure more workers Foxconn has had to offer bonuses and higher salaries.

In the videos, workers vented about how they were never sure if they were going get meals while in quarantine or complained that there were inadequate curbs in place to contain an outbreak.

"Foxconn never treats humans as humans," said one person.

Two sources with knowledge of the matter said there were protests at the Zhengzhou campus but declined to provide more details. They declined to be identified as they were not authorised to speak to media.

Foxconn and Apple did not respond to requests for comment.

"It's now evident that closed-loop production in Foxconn only helps in preventing COVID from spreading to the city, but does nothing (if not make it even worse) for the workers in the factory," Aiden Chau of China Labour Bulletin, a Hong Kong-based advocacy group, said in an email.

As of Wednesday afternoon, most of the footage on Kuaishou, a social media platform where Reuters reviewed many of the videos, had been taken down. Kuaishou did not respond to a request for comment.

The protest images come at a time when investors are concerned about escalating global supply chain issues due in part to China's zero-COVID policies that aim to stamp out every outbreak.

The curbs and discontent have hit production. Reuters last month reported that iPhone output at the Zhengzhou factory could slump by as much as 30% in November due to COVID restrictions. Read full story

Foxconn is Apple's biggest iPhone maker, accounting for 70% of iPhone shipments globally. It makes most of the phones at the Zhengzhou plant, though it has other smaller production sites in India and southern China.

Shares of Foxconn, formally called Hon Hai Precision Industry Co Ltd, have slipped 2% since the unrest emerged in late October.