Four Australian men and women as well as a South Korean woman were arrested in Sydney early Friday and charged with multiple offenses relating to a sex trafficking business that was making A$3 million (S$3.88 million) a year, Australian Federal Police and the Immigration Department said in a joint statement.

The victims, rescued by police Thursday, were receiving counseling and government support, Immigration official Lyn O'Connell said.

A decision has yet to be made about whether they would remain in Australia as prosecution witnesses, she said.

'This is alleged to be an organised syndicate where they are exploiting workers who are coming to Australia on lawful visa conditions,' Ms O'Connell told Australian Broadcasting Corp radio. 'The allegation is that they were forced to work ... in the sex industry in breach of the normal employment conditions,' she added, without elaborating.

Police allege the Sydney syndicate recruited women as prostitutes in South Korea by deceiving them about the work conditions and then organized their work visas.

Police Assistant Commissioner Tim Morris told reporters that the victims had agreed to work in the Australian sex industry 'under more reasonable conditions.' Once in Australia, the syndicate took the women's passports and made them work in a legal syndicate-owned brothel for up to 20 hours a day, the statement said.

Police have not said how long the women had been enslaved.

'This investigation has dismantled a highly organised syndicate and prevented more women from being lured into such terrible circumstances,' Mr Morris said in the statement.

The five people arrested, whose identities have not been released, face a range of charges including conducting a business that involves sexual servitude and dealing in the proceeds of crime worth more than A$1 million.

The proceeds of crime charge carries a potential maximum penalty of 25 years imprisonment while the sexual servitude charge carries a potential maximum of 15 years.

It was not immediately clear what potential sentence each defendant faces.

Police say sex slavery is rare in Australia by international standards. The victims are usually illegal immigrants.

Immigration Minister Chris Evans said in a statement the arrests showed that Australia is 'serious about preventing the insidious crime of people trafficking and the exploitation of women in the sex industry.' -- AP