New Zealand suffered one of its deadliest mass shootings nine months ago when a lone gunman killed 51 worshippers in two mosques. The government banned several semi-automatic weapons immediately after, and authorities announced Saturday that they have collected more than 50,000 guns so far.

Prime Minister Jacinda Ardern banned the most deadly types of military-style weapons less than a month after the attack in Christchurch. Police then launched a six-month buyback program to collect newly banned weapons from their owners — a method that was largely successful in Australia in the 1990s.

Ardern's fast approach earned public praise and almost-unanimous bipartisan backing. The buyback period ended at midnight on Friday, but many gun collection events ran late after a surge in last-minute returns, officials said in a statement.

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"Six months ago when we started the Firearms Amnesty and Buy-back, our challenge was to remove as many prohibited firearms as possible from our communities," the New Zealand Police wrote on Facebook. "NZ Police rose to the challenge, and today we want to thank the thousands of firearms owners who have done the right thing and together helped make NZ safer."

Firearms amnesty and buyback Six months ago when we started the Firearms Amnesty and Buy-back, our challenge was to remove as many prohibited firearms as possible from our communities. To do that we needed to create as many opportunities as possible for New Zealanders to do this. NZ Police rose to the challenge, and today we want to thank the thousands of firearms owners who have done the right thing and together helped make NZ safer. Deputy Commissioner Mike Clement and Minister of Police Stuart Nash speak on the amnesty and buyback. Posted by New Zealand Police on Friday, December 20, 2019

Authorities said over 33,000 people turned in more than 56,000 guns. Additionally, owners modified over 2,700 guns to be legally compliant, police seized 1,800 from gangs and are in the process of collecting 1,600 more from gun dealers.

Police Minister Stuart Nash told The Associated Press that it is common for criminals to steal assault weapons from lawful owners. With these weapons out of circulation, criminals would have a harder time finding weapons.

"I believe we've got the majority of these guns in," Nash told New Zealand's national broadcaster on Tuesday.

However, some gun owners are critiquing the buybacks, calling the process flawed.

Nicole McKee, a spokeswoman for the advocacy group Council of Licensed Firearms Owners, said many owners are illegally holding on to their firearms because they no longer trust the government and are not being offered proper compensation.

"They never overcame being blamed by authorities for being somehow responsible for a heinous act of terrorism — something they would never do," McKee said in a statement, AP reports.

Police said they do not know exactly how many guns were in the country, making it difficult to gauge the program's success. They are pushing for a better tracking system to monitor the rest of the guns in the country.

The government said it paid out just over 100 million New Zealand dollars ($66 million) during the buyback. Violators of the new ban face five years in prison.