ZHENGZHOU - A number of illegal brick kilns in Central China's Henan province have enslaved and abused mentally disabled workers, local media reported on Sunday.

Meanwhile, the practice of smuggling such workers has developed into a local business.

Public security departments in four involved counties and cities rescued about 30 enslaved workers on Monday and detained some of the kiln bosses and managers, said Cui Songwang, a reporter with the TV channel of City Report in Zhengzhou who exposed the scandal.

Cui disguised as a mentally disabled person near the Zhumadian train station and was sold to Wan Chengqun, a kiln operator in Zhumadian, for 500 yuan ($78) after he was taken on Aug 17 by two unknown men.

He managed to escape after he was abused and forced to work during a three-hour detention.

Yuan Junfeng, a publicity official with the police department of Dengfeng, one of the involved cities, refused to give more details and said they would release a written version of material on Tuesday.

China Daily's calls to police officials in Zhumadian, the other city, went unanswered on Monday.

According to the TV report, the number of slave workers in such kilns ranged from five to more than a dozen, and they stayed in stinking rooms. Some of the workers had been forced to labor for seven years without being paid.

They were given poor food and had limited rest amid heavy labor and frequent bullying by factory managers. Some of the mentally disabled workers also had physical disabilities, according to Cui.

The slave workers were bought, cheated or even abducted from the streets into such factories. Those who didn't obey the factory managers' orders were beaten until they "completely submitted", according to the report.

After heavy labor in such working and living environments for some time, the conditions of some workers worsened both physically and mentally.

Scenes in the TV report showed Wang Chengqun, an underground kiln owner, burst into laughter as he saw a new worker sent into his place.

According to insiders, the cost for hiring ordinary workers may be 20,000 yuan a year, while such slave workers were traded for 300 to 500 yuan between illegal recruiters and underground kiln owners, or among kiln owners themselves.

The practice of smuggling mentally disabled or other people as slave workers has existed in the province for at least 20 years, and areas including the train station of Zhengzhou were among the hard-hit ones.

The train station area was also blamed as the source of slave workers in a similar case in nearby Shanxi province in 2007 which shocked the nation. More than 20 illegal recruiters were arrested.

Though local authorities had promised to crack down on such deals and practices after the case, a recent investigative report by the Economic Information Daily pointed out that the station remained the way it was four years ago.

A local media staffer said such underground factories still exist in large numbers in the province, according to the report.