Motorcycle gangs are attempting to infiltrate police by joining up, union boss Greg O'Connor says.
And he is warning a budget freeze on the force will mean fewer gang members are weeded out at the recruitment stage.
O'Connor opened the Police Association's annual conference this morning with the stark warning.
''Police, particularly over the last four or five years, have been finding that when they do their checks of those seeking to join police that they have quite close links often to organised crime, particularly the gangs. We are talking dozens of people...attempting to join police,'' he later told reporters.
He added: ''We hope we've screened them all.''
He said the Headhunters gang had increased their numbers from 25 to around 92 ''and growing.''
''They are growing. They have moved into Upper Hutt. The Hells Angels have moved into Nelson. These are national crime franchises while we are inevitably retrenched,'' he said.
Attempting to infiltrate police was ''absolutely'' a deliberate strategy, and members kept dossiers on officers.
''Under a funding freeze every part of police is under pressure and that includes recruiting. Recruiting is being centralised to one or two pods and in the districts there won't be the scrutiny,'' he said.
O'Connor said no increase in the budget meant police must find $200m in the next two years and, potentially, $400m in the following two years.
''That can only come from one place - frontline policing - because it's a pretty lean machine already.''
He added: ''Clearly police with a frozen budget are going to have to be very particular about where that spending goes. Invariably the spending goes where the political expediency lies and that's around numbers.''
He told delegates that crime in New York had soared in the wake of funding cuts. It ''got on top'' of crime rates in the 1990s but had seen its first rises in 20 years.
''They are big rises. Double digits in many precincts and much of it in violent crime.''
New York police department had 6000 fewer officers than it did 10 years ago, he said.
O'Connor and other delegates also raised concerns about number of non-sworn staff losing their jobs - around 170 to date.
''With the cuts we are facing there are likely to be more,'' he said. ''The people go - the jobs don't go and someone has got to do it.''
Police minister Anne Tolley also addressed the conference this morning. She said new technology, better intelligence and prevention strategies were allowing investment in the frontline.
''They are getting really good information - it's about the policing in the right place at the right time...and using those police resources well and effectively,'' she told reporters.
''That's not a scatter gun approach, the way we might have done it 10-15 years ago. It's a quite different way of working. But yes it is a challenge...and gangs have an enormous effect in our communities.''
Labour's police spokesman Kris Faafoi said the Police Association's concerns need to be taken seriously.
"When the head of our Police Association raises the alarm about budget constraints adversely impacting the police recruitment process, we should listen," Faafoi said.
He said gangs were becoming more organised and were getting wise to technology ''to aide their criminal activity.''
"Budget cuts and staff cuts are leaving our police more vulnerable and are loading pressure on the front-line,'' he said.
"All the while we are told gangs are buffering their numbers and broadening their base. National's budget cuts are putting the integrity of the front-line itself at risk.''