(CNN) More than 10,000 firearms have been voluntarily surrendered to authorities in New Zealand as part of a buyback scheme that was introduced after the country's worst mass shooting in modern history.

As of Sunday, a total of 10,242 firearms had been handed in to police since the gun buyback kicked off on July 13, and another 1,269 had been handed in under amnesty, meaning people are able to anonymously hand in firearms with no questions asked -- even if they don't have a valid firearms license, New Zealand Police said in a statement Monday.

New Zealand has tightened its gun laws after a white nationalist allegedly opened fire at two Christchurch mosques on March 15, killing 51 people. The accused has pleaded not guilty to 51 charges of murder, 40 charges of attempted murder, and one charge under the Terrorism Suppression Act.

The suspect -- who used multiple guns in the attack -- obtained a gun license in November 2017 and began purchasing guns legally in December 2017, New Zealand Prime Minister Jacinda Ardern said.

The day after the attack, Ardern said the country's gun laws would change -- and two weeks after the attack, a bill to ban semi-automatic firearms was introduced to Parliament.

Under the buyback scheme which was brought into law in June and launched on July 13, gun owners have until December 20 to hand in semi-automatics, parts that convert firearms into semi-automatics, magazines over a certain capacity, and some shotguns. Gun owners are compensated, with each weapon allocated a pre-determined set price. The buyback scheme is expected to cost up to $200 million.

Already, more than 90 collection events have been held around the country, and 7,180 firearm owners have attended, police said.

"We have been really happy with New Zealand's engagement and response to this process and we look forward to more people taking part in the buyback scheme over the coming months," police said in a statement.

In New Zealand, gun owners require a license, but do not have to register their weapons, meaning no one knows for certain how many guns are in circulation. Police estimate there are about 1.2 million guns are in circulation in the country -- around one gun for every four people -- but they do not know how many are semi-automatics.

Many of New Zealand's gun owners are farmers or recreational hunters -- and some have criticized the government's swift gun control moves as "ill-advised."

Gun owners hand in their firearms at Riccarton Racecourse on July 13, 2019 in Christchurch, New Zealand.

How other countries compare

Australia also introduced a gun buyback after a shooter killed 35 people in Tasmania in 1996. The country's then-government recovered about 640,000 prohibited weapons, according to the Australian National Audit Office.

But New Zealand and Australia's approach contrasts with that of the United States, which has not introduced similar restrictions despite a long list of mass shootings.

Earlier this month, an alleged shooting at a Walmart in El Paso, Texas, left 22 people dead. In a document believed to have been written by the shooter, the suspect expressed support for the Christchurch attacks.