UPDATED 12:00pm: A fugitive couple wanted on fraud and sex charges are believed to have left the country using false passports.

The New Zealand Herald reports Paul Bennett and his Australian partner Simone Wright travelled the length of the country evading authorities, before eventually disappearing four months ago.

Police say the trail has gone cold but a private investigator hunting the couple has tracked them to Australia - and believes they used false identities to get out of New Zealand.

Bennett and Wright are wanted after allegedly swindling a helicopter firm out of $250,000 thousand dollars.

Police also want to talk to them about an alleged sex attack on a young girl.

It's the third case in weeks in which criminals have escaped New Zealand using false documents.

Businessman Mike Jacomb says he was cheated out of $250,000 by the pair. He's offering a $50,000 bounty to find them.

"He's had five passports and he's been in and out of the country at will. When I knew him, he would go to Europe, then he'd go to Australia a great deal, the border patrols are very very lax in New Zealand."