Some people knelt down in front of the city office and cried and begged authorities to release people

Protester

The protests, which have been underway in Liaoyang and another north-eastern town for several weeks, are being closely watched to see how authorities react.

Such protests are rare, especially in the heart of the Chinese capital, but they have become more common as China grapples with painful reforms of its state industry.

Earlier this month up to 50,000 retired oil workers protested in the north-eastern town of Daqing, and 30,000 workers demonstrated in Liaoyang, to demand unpaid pensions and wages.

In Liaoyang, the wife and daughter of one of the detained workers told the French news agency AFP that 500-600 workers and relatives of workers from the Liaoyang Ferroalloy Factory gathered outside the city government offices on Thursday.

"Some people knelt down in front of the city office and cried and begged authorities to release people. Even the elderly bent down on their knees," said Yao Dan, the daughter of arrested protester Yao Fuxin.

Key problem

In Beijing, the protesting retirees waited inside and outside the plant's gates, according to the Reuters news agency.

"Since 1999 they haven't reimbursed any of our medicine costs, 1999, 2000, 2001 - it's been three years," one retiree said.

The retirees were later reported to have met with company representatives but failed to resolve their dispute over years of overdue pension and health care payments.

The protests highlight a key problem in China's current welfare system - factories are often responsible not only for providing for their retired workers, but also for paying unemployment benefits to the same workers they have made redundant.

The government has acknowledged the problem poses a threat to social stability, and is in the process of setting up a national social security network.

The need has been made all the more urgent by fears that China's entry into the World Trade Organisation will lead to millions of new redundancies.

But setting up the new welfare system will take several years, and in some areas of the country, enterprises and local governments are currently struggling to keep up payments.

Suspicions of official corruption have exacerbated tensions among laid off workers.