Protesters clashed with police in central China during a demonstration by hundreds of people at a factory producing COVID-19 antigen kits, several videos posted to social media showed.

Online users said the protest was over wages and the layoff of several workers by the manufacturer, Zybio, in the central municipality of Chongqing.

Reuters was unable to obtain any immediate comment from Zybio, but verified, via geolocation, that some of videos were filmed at the company’s factory in Chongqing.

One video showed people throwing traffic cones, boxes and stools at police carrying riot shields. Another video, posted on social media platforms such as Twitter and Douyin, showed dozens of protesters chanting “return our money”.

A person who answered a phone call at Zybio’s headquarters declined to comment on Sunday. Emails to the company were not immediately answered.

Protests are not rare in China, which has over the years seen people demonstrate over issues such as financial scams or labour disputes.

But authorities have been on higher alert after a series of protests late last year, including worker unrest at Apple supplier Foxconn’s massive iPhone factory in central China, as well as widespread protests in Chinese cities and top universities against COVID restrictions.