A Government deadline to hand over banned firearms ends on Friday, amid claims that tens of thousands of guns are being hidden from authorities.

More than 56,000 firearms — including semi-automatic guns and firearms with large capacity magazines — have been collected by police as part of a gun buyback programme launched after the March 15 terror attack.

The buyback scheme ends on Friday evening. Police Minister Stuart Nash warned gun owners the clock was ticking to "stay on the right side of the law".

But the law's critics have decried the policy as a failure.

DAVID UNWIN/STUFF Firearms administrator Ethan Burmeister at a national firearm amnesty and collection event held at the Awapuni Racecourse last month.

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Council of Licensed Firearm Owners (Colfo), a lobby group for various firearm organisations, and ACT MP David Seymour fronted the press at Parliament on Friday morning to reiterate their frustration with the law.

They pointed to Government over-reach, a lack of consultation, and insufficient compensation for gun owners, among other complaints.

The Government in April announced semi-automatic firearms, many similar to those used to kill 51 people in the Christchurch terror attack, would be banned with sweeping changes to firearm law.

Firearm owners have since been asked to hand in their weapons for destruction at some 650 collection events, where they have received compensation amounting to 95 per cent of the retail value or less.

Under new legislation, anyone in possession of such guns could be jailed for five years.

SUPPLIED Colfo secretary Nicole McKee said firearm owners would be hiding valuable and heirloom firearms.

There are an unknown number of firearms in New Zealand's civilian armoury, and Government-advisors KPMG have estimated there could be around 170,000 now-banned guns owned by Kiwis.

Colfo secretary Nicole Mckee said this showed two thirds of prohibited firearms were not being handed in.

She said the lobby group had heard of people considering flouting the law, and the failure to collect so many had created "the biggest influx of criminals from law abiding people".

"There are quite a number of people out there that do not realise, they just think, 'I don't have a semi automatic', so I'm not caught up on this.

"They are just learning now some of the about the magazine capacities .... It's a real mess."

WARWICK SMITH/STUFF ACT leader David Seymour, who has opposed the "rushed" changes to firearm law.

​Colfo continued to insist its members hand over their guns, and their members would not be those acting unlawfully, she said.

The group wanted the Government needed to extend the buyback to be a year-long, and broaden the compensation scheme.

Seymour said the law change was rushed and conservative estimates indicated 20 per cent of prohibited firearms had been collected.

"The truth is, that we had a law-abiding firearm community who, in my view, have become engaged in civil disobedience on a massive scale because Parliament eroded the respect for the law."

Stuff Police Minister Stuart Nash said the clock was ticking for firearm owners.

Nash, in a statement released Friday, said there had been a last minute surge of firearm owners returning firearms.

"More than 56,346 prohibited and unlawful firearms have so far been removed from circulation ... This is within the range estimated by KPMG."

RICKY WILSON/STUFF The national gun buyback ends on Friday.

National Party justice spokesman Mark Mitchell said the Government should be blamed for a failed buyback scheme.

"The Government made a mistake in targeting law-abiding firearms owners when they should've targeted the gangs ... The result is a lot of confusion and lack of engagement."

National voted for the legislation in April.

A police spokeswoman declined to comment or provide an interview on the buyback's end.

Deputy Commissioner Mike Clement and Nash would speak on the buyback at an event in Auckland on Saturday.