Semi-automatic guns sold by the Defence Force to the public in the 1990s, are turning up in the hands of gangs and organised criminal groups.

More than 170 military-style, semi-automatic guns had been seized by police in the past five years.

More had been taken in each of the last three years than in any year in the past decade.

In a briefing to the Minister last year police said they were concerned that they had seized military-style guns from gangs and organised crime groups during searches.

They said gangs were starting to use a different type of firearm - the high-risk military-style guns used in massacres in the US.

The director of Otago University's National Centre for Peace and Conflict Studies, Kevin Clements, said these guns getting into criminals' hands was hugely concerning.

He said the guns had a huge lethal capacity in the hands of gangs and could cause mayhem.

"If the police are capturing larger and larger numbers of them then it means this [gangs and organised criminal groups] is where they're actually located."

Clements told Mike Yardley these guns getting into criminals' hands is a big concern.

"Instead of just shooting one person at a time they can actually shoot large numbers of people at a time, these weapons have the potential for creating mayhem and we want to make sure that doesn't happen."

He said New Zealand's current gun control laws have lots of loopholes.

"The Police are trying to do the best with a law that is very muddy and the gun owners, themselves, are trying to do all they can to circumvent them."

"If you take an automatic, military-style weapon, you can turn weapons which A category gun owners have, into those types of weapons just by adding different gun stocks to them. So you can actually turn a lot of A category weapons into E category weapons just by changing the stocks."

"More and more people are buying these things and importing them from overseas and the police are playing catchup a little bit to try and get a grip of who has got them in their possession."

In New Zealand, gun owners are registered but not the individual guns which makes it hard to track them, Clements said.

"There is no linkage between the actual gun you have got and the owner and that's a problem and the other problem is the procedure for moving from an A category registration to an E category registration is a little bit fluffy."

"Basically you can get an E category registration if a gun club says you're a solid and reliable citizen and you're not going to be subject to a psychotic break and so forth, so there's a little bit of confusion there around who should have access."