Beijing: Tens of thousands of workers were on strike today at a factory in southern China which makes shoes for Nike and Adidas, rights groups and a worker said.

More than 30,000 employees at the Yue Yuen Industrial (Holdings) factory in Dongguan city have been striking for several days in protest at unpaid social insurance payments, said US-based China Labour Watch, adding that police had beaten and detained several protesters.

China is facing labour unrest as its economic growth slows and as factories in its southern manufacturing heartland report a shortage of workers, prompting rising demands from staff.

Yue Yuen says on its website that it produces shoes for foreign brands including Nike, Adidas, Puma and New Balance. The factory at Dongguan in Guangdong province is partly Taiwanese-owned.

A spokesperson at Yue Yuen`s office in Hong Kong was not immediately available for comment, while Puma denied having a working relationship with the Dongguan plant in a statement to AFP.

The strike comes as the massive factory traditionally gears up production ahead of the summer season in Europe and the US.

"The workers are still striking, and the numbers have probably increased," said Dong Lin, a worker at the Shenzhen Chunfeng Labour Justice Service Department, a rights organisation in close contact with the workers.