She said SICU worked in conjunction with the Australian Federal Police's specialist human trafficking officers. "We do see indicators [of trafficked women] at times," she said.

According to Sergeant Ross the sex workers do not live in the apartments - instead the apartments are rented short-term, sometimes by a sex worker sole trader and sometimes by an 'employer' with several employees. Advertisements run on online classifieds sites. "They advertise on a number of different websites that are not only in English," she said.

Sergeant Richard Farrelly of SICU - who last year found an Asian woman hidden in a wall cavity in a Seaford brothel to avoid detection - said serviced apartments as well as rented apartments were an emerging trend in illegal sex work. "They offer everything from masturbation to full sex," he said. "The apartments are all relatively new, one to two bedroom apartments. It is literally as though you are walking into someone's apartment."

He said residents groups in residential towers were a key in helping police. "These places certainly impact on the amenity for the residents. They are usually open from ten in the morning until even midnight."

Sergeant Ross said the apartments were unhygienic and the sex-work unregulated. "It is these types of unregulated businesses which often mean that employees are working in exploitative conditions," she said