Legalised prostitution has encouraged foreign sex workers to move here without visas or residency because it is "low risk", a prostitute has said.
Kimmy, a prostitute from Seoul who works in central Auckland, said New Zealand was a "popular choice" because the laws were more "relaxed" and immigration penalties low.
She said working in her native country could land her in prison for a year or fined up to nearly $4000 under tough new laws.
"The risk is small here because the only law I am breaking are immigration laws, which is not so serious," she said.
"The risk to work in New Zealand is very much lower than in South Korea.
"The money is better too," she said.
Under the Prostitution Reform Act 2003, only New Zealand citizens and residents can work in the sex industry.
Those found in breach of their visitor permits could face removal.
In the last year, the visitor permits of eight sex workers have been revoked and others whose permits were close to expiry were told they would not be renewed, Immigration New Zealand said.
Seoul implemented a Special Law on Sex Trade in 2004, resulting in brothels having to shut down and millions of pimps forced to quit working.
Kimmy said many sex workers, who found it too difficult to work in South Korea, travelled overseas looking for work.
Nigel Bickle, head of Immigration New Zealand, said his agency had visited about 10 Auckland brothels in the last year, mainly to educate employers and brothel owners.
"Our compliance staff do monitor the sex industry for breaches of the Immigration Act," he said.
"The action taken will depend on the information obtained during an investigation."
Annah Pickering, the Auckland manager of the New Zealand Prostitutes Collective, said sex workers have been coming from Asian countries to work in New Zealand since the 1980s, and despite knowing some of them were here illegally, the collective does not discriminate.
"The collective has ongoing contact with these sex workers and recognises that, regardless of their legal status, it is important to ... provide them with condoms and information about ways to keep safe," Ms Pickering said.
She said Asian prostitutes outnumbered Maori and Pacific people, and was the second largest group behind Pakeha.