New Zealand ban on guns used in mosque attacks could come into effect next week as country initiates bill for law changes

Woman lays flowers on a wall at the Botanical Gardens, Christchurch (Picture: AP)

A New Zealand law that would ban the types of weapons a gunman used to kill 50 people at two mosques last month could come into effect next week.

If the bill passes as expected, police minister Stuart Nash said the law would take effect on April 12, less than a month after the mass shootings in Christchurch on March 15.

Plans for law changes were first announced by Prime Minister Jacinda Ardern in the days after the attacks, when the government imposed an immediate ban on the sales of such weapons.

The bill has bipartisan support and could even pass with a unanimous vote of all 120 MPs.

Jacinda Ardern announced the plans in the days after the terror attack (Getty Images)

"These are guns that are designed to kill people," Mr Nash said.

He said one of the weapons used by the gunman was an AR-15 style rifle, and that all the weapons the gunman used in the attacks would be banned.

The bill would ban "military-style" semi-automatic guns and high-capacity magazines.

An AR-15 style rifle displayed (AP)

It would also ban semi-automatic shotguns that could be fitted with detachable magazines, and pump-action shotguns that can hold more than five rounds.

The bill would not ban guns often used by farmers and hunters, including semi-automatic .22-calibre or smaller guns that hold up to 10 rounds, or shotguns that hold up to five rounds.

Mr Nash said the gunman had left a national legacy of harm, pain and grief.

He said the gunman was able to buy semi-automatic guns and high-capacity magazines legally, and then put them together to create military-style weapons.

"The loophole that this terrorist used to kill 50 people was totally unacceptable," Mr Nash said. "We're closing that down."

The bill would also impose tougher penalties for people who use the weapons after they are banned.

MPs intend to introduce more legislation later in the year, including the creation of a register to track guns.

The government intends to compensate owners of banned guns in a buyback scheme that will cost up to 200 million New Zealand dollars (£105 million).

An amnesty will give people until September 30 to hand over banned weapons.

There will be some exemptions from the ban including police officers, military personnel and some authorised pest controllers.