Police demonstrate how they destroy firearms that are handed in during the gun buyback and amnesty.

Police Minister Stuart Nash says there could be fewer guns in the country than experts have calculated.

His comments come as police data shows they could struggle to collect even the lowest estimate of banned guns, under a gun amnesty and buyback scheme, which ends on December 20.

An April ministerial briefing paper revealed that police estimated between 60,000 and 240,000 firearms would be made illegal under gun law reform and in September police suggested that number was between 56,000 and 173,000.

But police have not set any specific operational targets for the gun buyback scheme.

Official figures show that between July 13 and October 29 about 32,659 firearms were collected and more than $62 million had been paid out so far.

ROSA WOODS/STUFF Police Minister Stuart Nash suggests there may be fewer guns in the community than originally anticipated.

When the police data is crunched, it works out at an average of 282.43 banned firearms collected per day.

At the current rate, about 45,188 banned firearms would only be collected by the December 20 deadline. In order to meet the initial 60,000 estimate, police would need to collect about 600 firearms a day before the deadline.

A KPMG report that informed the pricing of the buyback scheme estimated the total number of all weapons, both lawful and prohibited, was between 1.2 million and 1.5m and there were about 14,300 military style semi-automatics MSSAs.

It calculated there were 760,000 rifles and 380,000 shotguns in the community but noted there was significant uncertainty around the number and condition of firearms in the community.

ROBERT KITCHIN/STUFF Police have previously estimated between 60,000 and 240,000 firearms will be made illegal under gun law reforms. Between July 13 and October 29, 32,659 firearms were collected under a gun amnesty and buyback scheme.

It warned that despite its best efforts, the report may not capture the full depth and breadth of the complex scheme.

Nash said the number of guns in the community was a great unknown, which was why a firearms register was needed.

'Maybe it is less than KPMG estimated … It was a rough estimate based on some modelling. Maybe KPMG got it wrong, who knows .... Maybe there are fewer guns in the community than originally anticipated."

He suggested that some gun owners may wait until the last week of the buyback.

Nash and the police are adamant the buyback will not be extended and have urged gun owners to hand in their firearms.

NEW ZEALAND POLICE Amnesty and gun buyback performance summary as at October 29.

His pleas were not meant to sound desperate and were an education so gun owners had no excuses, he said.

"I have been very clear that if people don't hand in the other prohibited firearms and parts by December 20, they will get no money and will face up to five years in prison and the loss of their firearms' licence."

A police spokeswoman said while the dealer hand in option would finish prior to December 20, public collection events would be held around the country right up until the end of the amnesty and buyback.

Police believed law abiding firearms owners would continue to hand their firearms in, she said.

NEW ZEALAND POLICE Amnesty and gun buyback performance summary as at October 29.

They had collected 4,408 MSSAs as of 29 October and knew how many were held legally and by who. They aimed to ensure that 100 per cent of those were accounted for as part of the amnesty and buyback but not all would be required to be returned or surrendered.

National Party police spokesman Brett Hudson said the Government risked its buyback scheme becoming a failure if it did not take swift action.

During a select committee this week police had defended the use of the model to estimate the potential number of guns in the country and prohibited firearms, he said.

HAMISH MCNEILLY/STUFF Superintendent Paul Basham discusses the first gun buyback held in the Southern region.

By the Government's own estimates, there were still 140,000 or more firearms yet to be handed in, he said.

ACT leader David Seymour said if the Government was not going to collect even a quarter of the 240,000 guns at the higher end, it had completely and utterly failed on the issue.

New Zealand Police Association President Chris Cahill said removing more than 30 000 of the most dangerous firearms from circulation would appreciably lower the risk of such firearms ending up in the hands of dangerous criminals and, therefore, made the country a safer place.

"The reality is that without a register since 1983, we have no real idea of the number of firearms to be captured by the buyback scheme. The only real figure is that for the Cat E registered firearms."