In the wake of the Texas church massacre, new information shows there are more than 13,000 military-style semi-automatic (MSSA) weapons in this country.
Information released to RNZ under the Official Information Act shows the weapons make up nearly a quarter of all restricted firearms in this country
Police said owners were vetted before they were allowed such weapons, and faced tougher security requirements than for a standard gun licence.
Police said this system dealt with any potential risks.
National Centre for Peace and Conflict Studies director Kevin Clements said 13,000 was far too many.
"Most of those weapons are absolutely no use whatsoever for either hunting purposes or farming purposes.
"They are, as their name indicates, assault weapons and developed primarily for military use."
Professor Clements said the 13,000 weapons were just the ones registered with police and the actual number could be higher still.
"You just need one individual, as in Aramoana, or one individual, as in Texas, who suddenly has a psychiatric break, or very malign purposes with access to such weapons, and then they can create mayhem.
"Then people will say, 'well how did he have access to such weapons?'.
"Well they had access to such weapons, because many of them are not under very strict control."
Professor Clements said there should be an amnesty similar to one in Australia following the Port Arthur massacre in 1996.
"I think the more that can be taken out of circulation the better."
Council of Licensed Firearm Owners spokesperson Nicole McKee said there were valid uses for the guns - such as hunting rabbits and culling goats.
"We also have legitimate sporting use for them as well.
"We have clubs ... such as [the] New Zealand Service Rifle Association, which use these types of firearm both nationally and internationally."
Mrs McKee said the number of military-style semi-automatic weapons in New Zealand was low given there were about 1,200,000 guns in the country.
There were strict processes in place to ensure the guns remained in safe hands, she said.
"The owner is checked on by police roughly every 12 months to make sure those particular firearms are still in their possession, so all those firearms are registered."
Police Association vice-president Craig Tickelpenny said MSSA guns were not the main problem.
"They're actually following the regulation and rules with the firearms licence system.
"The bigger issue really is unlicensed firearms, or the firearms being stolen out in the community," he said.
Mr Tickelpenny said registering firearms was the best protection against theft.