Tens of thousands of employees at a Chinese factory making shoes for Nike, Adidas and others returned to work Monday after one of the country's biggest recent strikes ended, following what campaigners called typical government intimidation.

The Communist Party fears an independent labour movement could threaten its grip on power, so it only allows one government-linked trade union.

But analysts say workers have been newly empowered by a labour shortage turning bargaining power in their favour, and the strike highlighted a wave of activism from older factory personnel nearing retirement.

The dispute broke out at a facility run by Taiwanese firm Yue Yuen, which says it is the world's largest branded footwear manufacturer, producing more than 300 million pairs of shoes last year.

The plant in Dongguan, in the southern Chinese manufacturing heartland of Guangdong, is one of the world's biggest shoe factories and has an estimated 45,000 workers, mostly women.

Vast numbers refused to work for nearly two weeks over unpaid social security contributions.

But after authorities ordered it to "rectify the situation" and it made small concessions, scores of strikers were detained by police, workers said, adding key demands remained unmet and they only returned because of intimidation.

"Police have arrested workers in the workshops for not working, more than 60 were detained," said one worker who did not want to be named for fear of reprisals. "At the moment the factory is controlled by police."

Six employees told AFP about four fifths of the staff had returned to work.

A 45-year-old sanitation worker surnamed Li added: "The workers were not successful, the government is forcing us back to work."

- 'Your life's work will be useless' -

According to Chinese law, employers are obliged to make monthly payments into workers' social security accounts, to help provide medical insurance and a pension. But analysts say manufacturers often shirk their responsibility.

"If you don't have social security, your life's work will be useless when you return home," said Li, who like nearly all the factory's workers comes from a poor rural village, where he one day plans to return.

Staff approaching retirement -- generally 60 for men and 50 for women -- led the strike, workers said, and thousands of protesters took to the streets before police forced them to stay within the factory confines, beating some staff.

"Our demands are not large. We simply ask for our social security payments and rent expenses to be paid for us," said a middle-aged worker surnamed Wang. A strike last year won a pay rise that took his salary to 2,800 yuan ($450) each month, he added.

After three days of the latest strike the factory offered a living allowance of 230 yuan per month, according to a company statement to the Hong Kong stock exchange. It also promised to make up for unpaid social security payments but said "the contributions cannot be quantified for the time being".

Wang added: "We have not been promised all our unpaid welfare statements. We have achieved one small result, getting the living allowance."

Activists say officials have become more sympathetic to individual grievances recently, especially those funded by foreign companies or investors from Hong Kong or Taiwan.

But such tolerance only goes so far.

During the dispute labour rights activist Zhang Zhiru, of the independent Chunfeng Labour Justice Service Department, was detained by police for four days.

"They told me not to communicate with the workers any more," he told AFP, adding that his colleague Lin Dong is still being held.

- 'Carrot and stick' -

Geoffrey Crothall, spokesman for the Hong Kong-based China Labour Bulletin, said the local government "put serious pressure on the workers to stop the strike and go back to work".

His organisation estimates disputes have surged 30 percent year-on-year in January-March, thanks partly to a labour shortage and strikers' increased use of social media to organise.

The government's response to the wave of activism varies depending on the scale of the strike, he added.

"Sometimes they'll be conciliatory, sometimes coercive, usually a combination of carrot and stick, which you see in this dispute.

"Once they get the employer to agree (to concessions) they put serious pressure on the workers to stop the strike and go back to work."

Neither Dongguan officials nor representatives of the Yue Yuen factory could be reached for comment by AFP.

A 17-year-old surnamed Tan said she earns around 3,000 yuan a month pressing accessories onto trainers -- including Nike Air Jordans -- at the plant and resumed work for fear of losing her job.

"Factory officials have warned us that those who make a fuss will be sacked without compensation," she said in a cafe near the factory's gates.

"The strike has failed, we didn't get the result we wanted."