Prime Minister Jacinda Ardern's government banned military-style semi-automatic weapons less than a month after a suspected white supremacist killed 51 people and injured 50 in a massacre at two mosques in Christchurch on March 15. Gun owners had until Saturday to return their firearms to receive a payout.

"As of midnight, 20 December 2019, 56,250 firearms and 194,245 parts have been handed in," Deputy Commissioner Mike Clement said in a statement.

Mark Mitchell from the opposing National Party said police failed to buy back "anywhere near the number of firearms it was aiming for."

As there is no gun registry in New Zealand, estimates of how many of the now illegal semi-automatic firearms were in circulation differ wildly.

While police earlier this year estimated that there were between 56,000 and 173,000 prohibited firearms, Mitchell suggested numbers were "as high as between 170,000 and 240,000 firearms."

In a statement, Nicole McKee, spokesperson of the lobbying group Council of Licenced Firearms Owners (COLFO), said the organisation believed that "two thirds of the firearms banned have been retained by owners."

Police Minister Stuart Nash on Saturday said the number of firearms handed in or still being processed was within the range estimated by consultancy firm KPMG which provided independent advice to police.

"However police have consistently warned the problem is we just don't know exactly how many guns are out in the community," Nash added.

Australian Associated Press