BEIJING - POLICE in Beijing have cracked a gang suspected of forcing nearly 100 women into sex slavery after giving them a 'training course' and requiring them to pass a 'hooker test', state media said on Tuesday.

At least 20 people have been arrested for allegedly forcing the girls to train as prostitutes and sending them to bathhouses, karaoke bars and massage parlours to work, the Global Times reported, quoting the police.

The gang was reportedly led by a 32-year-old man called Xie Zhaobin, who posted job ads in small newspapers in several Beijing districts last year, claiming to be looking for receptionists and PR workers, it said.

After a fake interview process, Xie's accomplices would allegedly confiscate the girls' IDs and he would then rape them and film the act, using the footage as leverage to force them to work as prostitutes.

Xie and his girlfriend Niu Xueying even provided a 'training course' for the girls, which sometimes involved the couple having sex in front of them to show them what to do and ended in a 'hooker test', the report said.

The gang allegedly received agent fees from the bars and clubs where the women were sent to work, and pocketed the girls' pay, making more than 500,000 yuan (almost S$97,000 dollars), according to initial police investigations.

Hookers' 'training' ring busted