"Whether a person migrated for a particular job or participated in an activity willingly is legally irrelevant under the UN Trafficking Protocol if they are subsequently kept in the service through force, threats, or psychological manipulation," he said.
Last year a sex worker who came on a visitor's visa told another prostitute at a central Auckland brothel where she worked that she had been made to work 16-hour shifts with few breaks.
Another sex worker who was lured here with a $4500 cash offer plus airfares was later told it was a loan she had to repay.
Both women had their passports taken away from them, and in one case the police had to be called in to retrieve the passport from the brothel owner.
But under New Zealand's definition, these did not constitute human trafficking.
"As most foreign trafficking victims have not yet fallen into the trap when they are in transit, border interdiction is less effective than interior enforcement, and diverts resources from the proactive field investigation that needs to be done in order to uncover this hidden crime," Mr Cdebaca said. He said robust victim identification practices should be made a top priority as victims rarely came forward.
The latest Trafficking in Persons report identified New Zealand as a source country for underage girls in sex trafficking and a destination country for foreign men and women in forced labour.
"New Zealand is reportedly a destination country for women from Asian countries, such as Hong Kong, Thailand, Taiwan and China, and Eastern Europe trafficked into forced prostitution," the report said.
"Child trafficking victims are found engaging in prostitution illegally in brothels and off the street, some being controlled by local gangs."
Mr Cdebaca said he stood by the findings of the report: "The Trafficking in Persons Report speaks for itself."
Immigration's general manager (risk and integrity) Steve Stuart defended New Zealand's definition of trafficking, and said it complied with international obligations as a signatory to the UN convention against Transnational Organised Crime and the associated Protocol to Prevent and Suppress Trafficking in Persons.
"While the cross-border element of our legal definition differs from other countries, we believe it is appropriate given our size and geographical location," Mr Stuart said.
"New Zealand has a strong stance on people trafficking and has comprehensive anti-trafficking legislation."
Penalties for trafficking in persons include imprisonment of up to 20 years or a fine of $500,000 or both.
The Crimes Act and Immigration Act also include measures to punish activities such as abduction, assault, kidnapping, coercing prostitutes and exploiting labourers.
