Zhu Hewei never imagined that slavery, a term printed in a history book, would become a grisly reality in his life.

The 28-year-old man came to Zhengzhou, provincial capital of Henan, in search for employment but was tricked by a human trafficker who claimed to offer him a job in a dye factory.

"When I followed them into a hotel, they locked me inside a room with a dozen others, some of whom didn't look mentally well," Zhu said.

Zhu didn't know he would then be sold to a shabby factory in the neighboring Shandong Province. And for the following week, Zhu was forced into tedious toiling in a filthy environment and without pay.

"The air was filled with dust, but we were given no protection. They fastened a wolfhound to the gate and installed cameras to prevent us from running away," Zhu said.

Zhu said most of the factory's 30 workers, with the youngest being 18 years old, were mentally disabled. They worked around the clock by turns to churn out a construction material.

Zhu was the only one who escaped. When the police arrived later, the boss had abandoned the factory, taking all workers with him.

Zhu's nightmare was among the latest slave scandals to hit China and revealed a nasty trade between the country's human traffickers and small factories that resort to slavery to survive amid a severe labor shortage.

The scandals also prompted a new round of police action, which freed 29 mentally disabled workers from illegal brick kilns in Henan. An underground supply chain was also discovered to have preyed on the country's mentally ill, migrant workers, and homeless children.

Fly over the cuckoo's nest

Last month, a local television station in Henan visited factories around the city of Zhumadian with secret cameras and exposed their brutal use of mentally disabled workers.

In a cramped, foul-smelling cabin, a worker was found to be half-blinded from severe beating. Others suffered shoulder and waist deformation after years of overwork.

They were neither paid nor given freedom to leave.

"I miss my home, but I have no money and they forbid me from leaving. Every time I attempted to escape they hunted me down, and then beat me severely," a worker said in the footage.

At corner of another factory, food was withheld from workers if they failed to fulfill the day's work.

One slave boss confessed, not knowing the real identity of the reporter, that his workers were purchased from the "agents," who priced the workers on their "qualities," such as the willingness to obey orders.

In order to uncover more details, Cui Songwang, a reporter from Henan Television, disguised himself as mentally disabled and roamed around the city's railway station, trying to mislead human traffickers.

After days of smoking discarded cigarette butts and eating leftovers at snack stands, Cui was thrust into a taxi by two human traffickers who sold him to a kiln called "Hengtai" for 500 yuan (78 U.S. dollars).

In the next three hours, he was ordered to drag a cart of materials, while being flogged with belt and denied water and rest through the process, Cui told Xinhua.

Cui said he might have been kept longer if the production was not halted by a mechanical glitch, allowing him sometime to fetch water. He seized the chance to flee the site and was later rescued by other reporters.

Yet Cui regretted that he failed to activate the secret camera he threw onto the factory ground, he said. "They watched me too closely. Otherwise, there might be more lurid details."

Underground supply chain

After Cui's investigation was broadcasted, police in Zhumadian raided the city's nearby factories and freed 17 enslaved workers, though the boss of Hengtai had absconded with his workers before police arrived.

Yet the police report much difficulty in tracing the human traffickers and illegal agents.

"They have woven a complicated network and committed crimes in such a covert manner that without reports it's very difficult to arrest them," said Chen Li, a police officer at Zhengzhou Bureau of Public Security.

Chen said the swindlers usually roamed around the city's railway stations, tricking job seekers with false offers, sometimes taking the vagrants by force. Some victims were directly sold to local buyers, while others were sent to slave agents who distributed them to factories around the country.

Even some unlicensed taxi drivers had joined the trade, sending ignorant job seekers to sweatshops to earn middlemen fees, according to the police.

Police recently busted an illegal agency in Zhengzhou after receiving reports from parents of three enslaved children workers.

The three boys, aged 13, 14, and 15, were cheated by the agents who found them wandering in Zhengzhou after dropping out of a boarding school.

They were then sold three times in 44 days to bag making workshops in the neighboring Hebei Province.

"The boss said he had spent quite a lot buying us and threatened force if we couldn't give him for his money," said one boy. All of the three boys had been subject to physical and verbal abuse.

The use of slave workers was brought to the spotlight in 2007, after a brick kiln in Shanxi Province was found to have enslaved 32 workers, one of whom died and 18 others suffered injuries due to their harsh work conditions.

Last year, pictures of mentally disabled workers drudging at a factory in Xinjiang again shocked the nation. The 12 rescued workers were found to be supplied by an illegal asylum in Sichuan Province that sold disabled people under its care around the country.

Experts said at the root of the slave scandals was the survival struggle of many small, labor-intense factories that featured poor work conditions and low salaries, at a time when China updated its industry and improved the welfare of its workers.

"That the supply chain couldn't be eradicated is because the demand runs high," said Shi Pu, a professor at Henan University of Economics and Law.

"It's both an economic problem and the result of a failed social administration," Shi said.

As of Wednesday, media reports have prompted police in Henan, Hebei, and Shandong to promise that a joint campaign will crush the nationwide network and search for more enslaved victims.

Efforts will also be made to restore order to local job markets and to arrest and eliminate illegal agents, they said.