"Any semi-automatic weapon used in the terrorist attack on Friday will be banned," Ardern said Thursday at a news conference in Wellington, New Zealand. "This legislation is urgently formulated and introduced."
Ardern said she hopes the bill will come into force by April 11. Weapons owners who want to give up their weapons have been encouraged to do so now.
Ardern said the "worst act of terror on our shores" exposed a number of weaknesses in the New Zealand weapons laws and promised that "Within 10 days of this terrible act of terrorism, we will announce reforms that I believe will make our community safer become."
"An amnesty is set up for the delivery of weapons The Cabinet has instructed officials to develop a buyback program," she said, adding that details of the buyback would be announced "in due course".
"I firmly believe that the vast majority of New Zealand's legitimate gun owners will understand that these steps are in the national interest and will take those changes in their path," she said.
The Australian Model
Police Minister Stuart Nash said the bill would include "tight exceptions" for the police and military forces as well as "legitimate business uses" such as professional pest control.
"Some guns serve legitimate purposes in our peasant communities," he added, noting that exceptions had been made for .22 caliber rifles and shotguns for duck hunting.
Immediate action would be taken to prevent people from stockpiling weapons before the law was changed and to encourage gun owners to give up their weapons, he said.
As part of the reforms, the mass shootings in Australia fell to zero, the suicides of weapons fell on average by 4.8% per year and gun-related killings by an average of 5.5% per year.