(Photo: VCG)

Gun owners in New Zealand have turned in more than 10, 000 firearms since the introduction of a buyback scheme just over a month ago, according to a CNN report.

The move came under tightened gun laws after a gunman opened fire at two mosques in Christchurch and killed 51 people in March.

Owners have until December 20 to hand in their semi-automatics, parts that convert firearms into semi-automatics, magazines over a certain capacity, and some shotguns for a compensation.

The buyback scheme is expected to cost $300 million NZD ($200 million), according to New Zealand Deputy Prime Minister Winston Peters.

Police estimate there are about 1.2 million guns circulating in the country, according to the CNN report.

New Zealand Prime Minister Jacinda Ardern promised "our gun laws will change" after the shootings and said she cannot understand why the United States does not ban semi-automatic guns, even after several mass shootings.

"Australia experienced a massacre and changed its laws. New Zealand has had its experience and changed its laws. To be honest with you, I don't understand the United States," Ardern told CNN's Christiane Amanpour.