Investigating the trade in sex slaves is difficult, time consuming work that needs the support of multiple police forces, Home Affairs Minister Brendan O'Connor says.

He was speaking after the ABC Four Corners program on Monday night revealed details of how criminal gangs lure women to Australia and then force them to work as sex slaves in legal brothels in Sydney and Melbourne.

"We know that the numbers of trafficking victims in Australia remains relatively low but more needs to be done," Mr O'Connor told ABC radio on Tuesday.

There have been just over 300 assessments or investigations by the Australian Federal Police since 2004, and from that just 39 cases were sent to prosecutors and only 13 convictions were achieved, he said.

"That turns on the lack of evidence," Mr O'Connor said.

"The law enforcement agencies in this country work closely and have to continue to work ever more closely.

"It's not the case any longer that you'll just have criminals operating within one precinct or one state or even one country. So that there is, of course, a stronger cooperation between agencies, both within Australia and beyond its shores, and that's critical."

Greens Senator Sarah Hanson-Young on Tuesday called on the federal government to take immediate action to protect the victims of sex trafficking.

She plans to write to Immigration Minister Chris Bowen to ask that urgent consideration be given to getting the women out of sex slavery.

"Women tricked into becoming sexual slaves need assistance such as temporary visas and support services to help them work through their ordeal and achieve justice," she said in a statement.

"All the constant noise over border protection and asylum seekers should be put into the proper context, because while these enslaved women are trafficked here under the radar, their plight is not given the attention it deserves."

The Australian Sex Party said the problem could be fixed in a year if the federal government abandoned its "morality agenda".

"If you eliminate the middle man by allowing bona fide sex workers to legally come and work in this country, like US computer programmers or Zambian Catholic priests, then you take away the framework of sex slavery and it collapses," party president Fiona Patten said in a statement.

Source: 9 News