A massive protest erupted at a factory manufacturing COVID-19 test kits in an inland Chinese city on Saturday, apparently resulting from a slump caused by a sudden change of the country's coronavirus policy.

Hong Kong media reported that more than 1,000 workers clashed with police over lay-offs and wages in Chongqing.

Footage released by Reuters on Sunday shows people believed to be workers yelling and throwing objects at police.

China ended its strict "zero-COVID" policy, and health authorities no longer conduct PCR and antigen tests from Sunday.

Testing is now limited primarily to medical workers and patients who have developed fevers.

Antigen test kits were in short supply last month amid the spread of infections across the country. But the prices have fallen recently as supply stabilizes.