About 1500 gun owners have contacted police since yesterday, when Prime Minister Jacinda Ardern announced a ban on military style semi-automatic rifles, to report ownership of such weapons.
Police said today they had received 474 calls by 11am, less than 24 hours after the ban was announced and an 0800 number was established.
Even more people have contacted police through an online form at the police website. However, some of those forms were "fake", wasting precious police resources, Police Assistant Commissioner Tusha Penny said in a statement.
"While these individuals may be short of productive work to do, police are not," she said.
"In the current environment, this is unacceptable."
Ms Ardern announced the ban yesterday in direct response to the Christchurch terror attack last Friday that resulted in 50 deaths of people worshiping at two mosques.
"The attacker took a significant number of lives using primarily two guns, assault rifles purchased legally on an A class licence," the Prime Minister said.
"The time for the easy availability of these weapons must end, and today it will...In short, every semi-automatic weapon used in the terrorist attack on Friday will be banned in this country."
High-capacity magazines and attachments will also be banned, and a buyback scheme has been promised for the firearms.
"The details of this [buyback] are being worked through now and information on how that will work will be announced in due course," Ms Penny said today.
"In the meantime, police encourage all affected people to log their information on the police website to ensure you can take part in the buyback."