Tonga's new police chief says a practice of clearing convicted criminals to travel overseas began with official sanction many years ago.
Grant O'Fee, Tonga's police commissioner, has told Radio Australia's the policy was put in place by a Minister who has since passed away.
"It was an unwritten policy that he could effectively clear the record of people at his discretion," he said.
"He delegated that authority without any written delegations to senior police officers and told them that they were entitled to do the same thing."
Mr O'Fee, who was appointed in July last year, says the policy carried on for ten years to 2011 and was only drawn to his attention last November.
He says at least 172 Tongans with criminal convictions had police officers write them official letters lying about their convictions so they could move to Australia, New Zealand or the United States.
The New Zealand Immigration Minister says an estimated 40 of those people may currently be in New Zealand and some may have gained residency.
Others are believed to have made their way to Australia.
New Zealand has put an immediate hold on Tongan visa applications that require police clearance.