A wave of foreign prostitutes working in breach of their visas is taking work from locals, sex workers say.

Photo: AFP

While some women advertising on sex work websites as foreign visitors would have residence or citizenship, immigrants now outnumbered New Zealanders in the industry, Christchurch prostitute Amber O'Hara* said.

"The New Zealand sex industry is now on a quite predictable trajectory, containing mainly illegal sex workers willingly travelling here to work from countries where it is illegal," she said.

"Yet it's a see no evil, hear no evil, speak no evil situation from those with the actual power to help."

Immigrants taking New Zealanders' jobs would not be allowed in other industries and the country was seen as a soft target for women who could makes thousands on a sex work holiday, Ms O'Hara said.

One of the main sex work websites advertised more than 800 women, separated into Asian and non-Asian prostitutes.

A registration scheme on sites would mean only those eligible to work could advertise - and ensure everyone was paying tax, Ms O'Hara said.

"It will mean that New Zealand ladies who do want to work, who are straight with the IRD and trying to do the right thing, can actually run a sustainable business without unfair competition from people who are not doing the right thing by our law.

"It wouldn't be a problem if there were just a few fly-by-nighters but, if you count the ads, New Zealanders are easily outnumbered."

Other prostitutes RNZ spoke to said they were being crowded out and undercut by immigrant sex workers, who were charging half the rates of their New Zealand counterparts.

Hamilton sex worker Lisa Lewis said most people who went on holiday maxed-out their credit cards.

"These girls are leaving with their credit cards in credit," she said.

"It's definitely a disadvantage for any legal sex worker because we are having to pay tax, the provisional, the income, the GST, ACC levies.

"They are leaving New Zealand without any of that taken off them, which is robbery of the government."

Ms Lewis had offered to meet with immigration minister Iain Lees-Galloway to discuss what was happening.

A spokesperson for Mr Lees-Galloway said his office had responded in detail to correspondence from Ms Lewis and passed on information from her to Immigration New Zealand.

*Not her real name.