Police have seized hundreds of military-style firearms in raids on gun dealers and collectors.
They believe the powerful automatic and semi-automatic weapons were destined for gangs and other criminals.
Fifty-five gun dealers and collectors were raided in Auckland, Waikato, Bay of Plenty, Hawkes Bay, Palmerston North, Wellington and Christchurch.
More than 500 weapons were confiscated.
Six people have been arrested on firearms charges and more arrests are expected. Charges relating to drugs have also been laid.
Some of the firearms were believed to have been imported illegally. Many appeared to have arrived after gun legislation was toughened in 1993.
About 20 per cent of the items seized yesterday had been illegally obtained and held, said Detective Senior Sergeant Mike Whitehead of Hamilton.
He was appalled at the number and type of restricted weapons involved.
"I've been a police officer just on 35 years and I must say I'm a little bit shocked to see the number of firearms that people lawfully hold."
If prosecutions against the dealers and collectors involved succeeded, Mr Whitehead said, police would seek to have all the weapons destroyed.
This would be regardless of whether some were registered with police and therefore held lawfully.
Successful prosecutions would result in the owners no longer being considered "fit and proper" people to hold such weapons.
The investigation began in August when police obtained information about a trade in unregistered firearms, Mr Whitehead said.
"We have established that some of these firearms have been sold to people who do not hold firearms licences or who have previously been prohibited from holding a firearms licence or owning firearms."
He said distribution of the weapons was organised on the internet.
The inquiry was based on two principal people and those who had dealings with them.
"They were selected to give us a snapshot of the collector and dealer environment."
The seized weapons include AK47s, Israeli Uzis, a Heckler and Koch MP5 submachine gun - used by anti-terrorist units around the world - a G3 automatic rifle, M4 carbine assault rifles, an AK74M, a Saiga 12 gauge eight shot, and Glock 17 pistols, used by police and military in more than 50 countries.
If sold lawfully, some of these items would cost between $5000 and $7000. But they could be worth 10 times more on the black market, Mr Whitehead said.
A process to revoke the licences of the dealers and collectors involved began last night.
International anti-gun lobbyist and former New Zealand television presenter Philip Alpers said the fact collectors had been targeted was a worry.
Collectors would have been heavily vetted by police and would never have been in trouble with the law before.
By and large they were a group of exemplary, reputable, safety-conscious people, Mr Alpers said.
"They are well known to police, and are often used as expert witnesses. They are a small, privileged group, many of them elderly.
"Collectors have for many years been seen as law abiding and exempt, so for these arrests to have happened something has gone seriously wrong."
Robbers' choice - Sawn-off shotgun
New Zealanders own more than one million guns, according to police.
Last month, they said New Zealand has a good gun-safety record but admitted they had no idea how many firearms were in the hands of criminals.
The figures were released as Parliament's law and order select committee considered the Arms Amendment Bill, which proposes tighter gun controls.
Police said firearms were involved in 621 violent offences last year, less than 1.3 per cent of all violent offending.
An independent review in 1997 of firearms control in New Zealand found:
* The favoured weapon for robberies is the sawn-off shotgun - the cheapest illegal gun at around $100.
* Handguns are used in crime to a greater extent than their proportion of the national armoury.
* Guns used in domestic violence are mostly owned by the offenders, but guns used for other criminal purposes are generally stolen.