Scores of workers have clashed with police at a Covid test kit factory in China, video spreading on social media showed Sunday, as the country navigates a path out of its hardline virus policy.

Footage geolocated by AFP to an industrial park in the southwestern city of Chongqing shows people tossing crates at a group of uniformed men, sending a shower of what appear to be test kits flying.

Another clip shows a crowd in front of a line of police at night as loudspeakers play a warning demanding they "cease illegal activities".

A man who posted video from the scene said in an accompanying caption that many workers had not been paid.

Other posts alleged that Chongqing-based pharmaceutical company Zybio suddenly fired workers who had been recruited in recent weeks.

Zybio did not immediately respond to calls from AFP, while the local police department declined to comment.

"All the workers' demands are economic in nature," said a man in one video who called himself a "Marxist-Leninist-Maoist". He insisted there was no political motive behind the protest.

AFP could not confirm exactly when the videos were captured, though multiple social media users said the clash took place on Saturday night into Sunday morning.

Distinctly patterned brown-and-white industrial buildings can be seen in the background of the videos, matching previous images of Zybio's facility in the Dadukou District Jianqiao Industrial Park.

The hashtag "Chongqing Dadukou Pharmaceutical Factory" appeared to be censored on the popular Weibo social media platform Sunday, with only one post from the previous day still visible describing the protest as an "interesting topic".

One video posted on a TikTok account belonging to a state-owned news outlet showed what it claimed was a street littered with antigen tests in a Chongqing industrial park.

"Sources say a labour dispute triggered conflict," the caption read. The video was taken down within hours.

Covid-19 infections have soared across China as the government moves away from its zero-tolerance approach to the virus, prompting a spike in demand for testing kits and drugs.

Authorities last month took over production lines at more than a dozen pharmaceutical firms, while some companies brought on new hires to meet surging demand.

Protests centred on labour issues and targeting individual companies occur frequently in China despite official efforts to clamp down on unrest.

Similar scenes unfolded at iPhone maker Foxconn's factory in central China last year, as furious workers unhappy with a Covid lockdown and pay dispute clashed with police.

China's strict Covid curbs sparked some of the country's worst unrest in years in November, with hundreds taking to the streets nationwide against lockdowns and mandatory testing.

The virus curbs were relaxed soon after the protests.