A review of prostitution laws by the Queensland Crime and Misconduct Commission found 20 per cent of that state's legal brothels were staffed exclusively by Asian-born women. And police intelligence suggests an even higher proportion of illegal prostitutes are Asian.

The situation is the same in other states, a finding of the review that is backed by research from the University of NSW.

''The number of Asian sex workers has definitely increased in the last 10 years,'' Christine Harcourt, author of The Law and Sexworker Health Project, said.

More than 50 per cent of women working in Sydney brothels are Asian. There is no suggestion of any sex trafficking.

''[Asian woman] are very much in demand,'' Dr Harcourt said. ''They're very attractive women, they're very good at their work.''

Kelly's Asian Flowers at Five Dock, an Asian-only brothel, urges men to ''take yourself on a journey to the place where only concubines and eunuchs were allowed and you are now the emperor and can choose your delight for tonight''.

But the national sex workers association, the Scarlet Alliance, said there was no evidence an increasing proportion of prostitutes were Asian. Elena Jeffreys, from the alliance, said the emergence of Asian-only brothels was a ''reorganisation of the industry''.

Former NSW sex industry consultant Chris Seage, who now runs Brothel Busters, which investigates illegal brothels for local councils, said nearly all illegal brothels in Sydney were owned or operated by Asians. He believes legitimate sex workers are an even mix of Caucasian and Asian-born women.

He said Asian prostitutes charged as little as half the fees of Caucasians and were more likely to have unprotected oral sex.

''What these places are doing is offering natural [unprotected] services, cheaper, with Asian girls,'' Mr Seage said. ''There is also a fantasy thing, especially with Aussie males. They want to try something different, something exotic.''

The owner of two all-Asian brothels in Sydney believes price is the main reason men visit her establishments. ''It's competitive,'' said the proprietor, who asked not to be named.

''There are quite a lot of Asians working … customers want to see Asian lady in the shop, they like the Asian lady, their appearance.''

Mr Seage said an hour with a Caucasian woman at a Chatswood brothel would cost $300; it would cost $150 with an Asian woman at a brothel in Willoughby.

Dr Harcourt agreed that sex with Asian prostitutes was likely to be cheaper. ''Most [Asian prostitutes] offer a lot of service for less,'' she said. ''Australian-born sex workers are usually pretty choosy.''

Some women from Hong Kong, Thailand or Korea come from poor backgrounds and have little English or skills, making prostitution a well-paid, flexible work prospect, Dr Harcourt said.

She said there was no clinical data showing higher rates of sexually transmitted infections among Asian sex workers.