Police are investigating nearly 50 false New Zealand passports, discovered during checks being done before a new online passport renewal system is introduced this year.
New Zealand passports are highly sought after by local and international criminal networks, and the 47 false documents found last year were many more than usual in recent years.
Documents released under the Official Information Act reveal the discovery was made because the Department of Internal Affairs is introducing an automatic process to enable adults to renew passports online next year.
In a bid to "cleanse" the database before online renewal begins, 4.5 million passport photos were matched against each other by facial recognition technology - a total of 21 trillion biometric checks.
Of those, 210,000 possible matches had to be checked by human eyes and most were discovered to be clerical or imaging errors or identical twins.
But the checks found 47 false passports.
Department of Internal Affairs general manager of passports David Philp said most passport fraud was committed by New Zealand citizens who had genuine passports but sought another in a fake identity.
"That could be for a whole lot of reasons," said Mr Philp.
"They may want to travel to a country where their criminal record may stop that, they may want to travel to a country where they have convictions, or they're involved in financial fraud or organised crime."
The introduction in 2003 of data-matching with the deaths register - so passports are automatically cancelled when someone dies - had led to a marked decrease in the number of false passports, Mr Philp said.
In the six years before 2003, there were 288 cases. In 2003, there were 41 and since then, only 162.
Today's passports, which have an electronic chip, were harder to forge than the old-style documents. Passports must now be renewed every five years, which Mr Philp said reduced the likelihood of fraud.
New Zealand's reputation as a law-abiding nation makes its passports valuable to criminals.
"A person carrying a New Zealand passport doesn't seem a threat internationally," Mr Philp said. "We're not a high-risk country, and we don't get the scrutiny that others do."
The biometric matching has already led to one man being convicted. Yaumeng Lum unlawfully obtained legitimate documentation belonging to Malaysian-born New Zealand citizen Peter Hui, and used it to obtain a passport in that name.
Twice he reported the Hui passports lost, and they were replaced.
He also used the Hui identity to change his name by deed poll to Thongviboon, and obtained another passport. In total, Lum travelled on the false passports nine times, including to Hong Kong, Singapore and Australia.
The Herald has learned Lum is also known as Paul Kwek Min Ou. He was sentenced to 10 months' home detention last August.
2011 - 47
2010 - 10
2009 - 28
2008 - 12
2007 - 14