The operation began after thousands of riot police surrounded a paint shop and an adjacent building at the Ssangyong Motor plant in Pyeongtaek, 70 kilometres south of Seoul.

Hundreds of workers - armed with metal pipes, slingshots and inflammable paint thinner - have occupied the factory since 21 May to protest job cuts designed to save the company.

Witnesses said two helicopters sprayed liquid tear gas. Police removed barricades with forklifts to help commandos climb ladders through a hail of nuts and bolts fired by slingshots.

Strikers also hurled firebombs or rolled out burning tires but failed to stop police reaching the rooftop of a building attached to the paint shop, where unionists have holed up.

Police then tried to move into the paint shop but retreated after a brief clash following fierce resistance from the strikers.

More than 500 unionists were still inside the paint shop, which contains stacks of inflammable materials. Hundreds of firefighters were on standby.

Three days of talks between managers and union leaders broke down on Sunday, raising concerns the debt-stricken company may file for bankruptcy.

The firm in February secured court protection from creditors after its Chinese investors - Shanghai Automotive Industry - gave up management control. Court-appointed managers have since struggled to turn it around through job cuts and cost savings.

The programme calls for the sacking of 2646 workers or 36 percent of the workforce. About 1670 of these have taken voluntary redundancy but others began an occupation of the plant.

Creditors have threatened to push for bankruptcy against the loss-making plant. But the union has refused to give up its demands for no layoffs and no lawsuits against it for damages.

The standoff has cost about 316-billion won (R2.01-billion) in lost revenue. The country's smallest auto firm specialises in sports utility vehicles and luxury sedans.