The latest reports come as the slavery ring that was initially reported only in Shanxi and Henan provinces in north and central China had in fact been operating elsewhere around the country for as long as a decade.

According to the government, police have so far rescued up to 570 enslaved workers, some of them children, and detained nearly 170 people suspected of trafficking, beating and enslaving workers in Shanxi and Henan. Tens of thousands of police have descended on thousands of brickyard kilns, small mines and metal-works factories in the two provinces, after the scandal made national headlines last week with the first arrests.

As authorities focused on ending the slavery, a report in the Communist Party magazine "Democracy and Law" said some female slaves had been forced into prostitution.

Two girls aged 17 and 16 had been forced into prostitution at the Wangjiang brick factory in Hebei province, immediately to the north of Henan, in 2004, according to the report that was picked up by the Xinhua news agency.

The girls were lured from their village in Shaanxi province with the promises of high wages and good jobs at a tile factory in early 2004, but soon discovered they had been tricked.

At first the girls worked alongside other laborers 16 hours a day, receiving regular beatings for not working hard enough, it said.