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 labourers 16 hours a day, receiving regular beatings for not working hard enough, it said.

But soon the brickyard boss began prostituting the girls to the workers, many of whom were handicapped or mentally ill, deducting portions of their meagre salaries each time they took one of the girls, it said.

Meanwhile, the China Daily newspaper said factories had been operating as far south as Guangdong province where workers had received tiny salaries but complained of routine beatings and unsanitary and prison-like work conditions.

Xinhua said in an earlier report that one man lost a toe from frostbite after running barefoot to escape a labour camp in China's far northeast Heilongjiang province.

During a press conference Tuesday, the police ministry vowed to crackdown on violations of labour rights and addressed accusations that local police in Henan and Shanxi had previously refused to investigate the brickyards despite desperate pleas by the parents of missing children.

"The attitude of the Public Security Ministry is clear, if we find any instances of dereliction of duty in the police force we will investigate and severely deal with it," ministry spokesman Wu Heping said.