South Korean police commandos have dropped from helicopters to try to end a factory sit-in by sacked workers demanding to keep their jobs.

More than 500 workers have occupied the main car plant of Ssangyong Motors for more than 10 weeks, the BBC reported Wednesday.

For a second day, police battled laid-off workers armed with metal rods and throwing projectiles.

Ssangyong is under court-approved bankruptcy protection and is trying to cut thousands of jobs to stay afloat.

Police said about 50 people were injured in Wednesday's clashes.

The commandos dropped by rope from helicopters while others were lowered in a shipping container onto the roof of one of the paint shops. Other police commandos charged the building with ladders.

The police cleared most of the factory at Pyeongtaek, 70km south of Seoul, but a hard core of workers remained in one of the paint shops at the complex, officials said.

Police have been worried about sparking a fire at the paint shops, where highly-flammable materials are stored.

Ssangyong has laid-off more than 2 600 workers, about one-third of its labour force. About 1 600 have accepted voluntary redundancy but the others decided to occupy the plant.

Negotiations to end the occupation broke off on Sunday, with the union representing workers rejecting a management proposal to reduce the number of layoffs. The union insists that no workers should be dismissed.