The government has also immediately implemented a stop-over measure that will keep the weapons being sold until the new laws can be implemented.
An amnesty would be put in place for the weapons to be handed in, with a buyback scheme to be announced soon, at an estimated cost of $NZ100 million to $NZ200 million.
New Zealand’s government will next week also consider tightening licensing rules and ammo restrictions. A gun register is also being mulled.
Concerns have been raised about the availability of military-style semi- automatic rifles after the man charged over last week’s attack, 28-year-old Australian Brenton Tarrant, allegedly used two of the weapons, legally bought with a licence, in the attack.
There are an estimated 1.5 million firearms in New Zealand – roughly one for every three citizens and more than double the rate in Australia.
Under the old law pest control was legally considered a reason to own a military-style semi-automatic weapon and there were no restrictions on the number of guns or ammunition a person could own.
New Zealand’s leader of the opposition, Simon Bridges, is expected to address media soon but this week has said he remained open to changing gun laws.
A petition signed by 65,000 people calling for a ban on semi-automatic weapons was delivered to New Zealand’s parliament earlier in the day.
The assault-ban announcement comes as the bullet-riddled Al Noor mosque in Christchurch underwent repairs ahead of Friday prayers and grieving families buried more victims of New Zealand’s worst mass shooting.
Ardern also announced that Friday’s call to prayers for Muslims will be broadcast nationally and there will be a two minute silence.
Armed police have been guarding mosques around New Zealand after 50 people were killed last Friday by a lone gunman who attacked worshippers at two mosques in Christchurch.
“We will have a heightened presence tomorrow in order to provide reassurance to people attending the Friday call for prayers,” police said in a statement on Thursday.
“Police have been working relentlessly, doing everything in our power to gather all appropriate evidence from what are active crime scenes so we can allow people to return to the mosques as quickly as possible.”
Both mosques attacked, the Al Noor and nearby Linwood mosque, plan to be reopened. Thousands of worshippers are expected at the Al Noor mosque, where the majority of victims died.
Most victims were migrants or refugees from countries such as Pakistan, India, Malaysia, Indonesia, Turkey, Somalia, Afghanistan and Bangladesh.
An Australian suspected white supremacist living in Dunedin, on New Zealand’s South Island, has been charged with murder following the attack.
He was remanded without a plea and is due back in court on April 5, when police said he was likely to face more charges.
The first victims were buried on Wednesday and burials continued on Thursday, with the funeral of a school boy.
Families of the victims have been frustrated by the delay as under Islam bodies are usually buried within 24 hours.
A mass burial is expected to be held on Friday. Body washing will go on through the day and night to have the dead ready for burial, said one person involved in the process.
Police have identified and released to the families the bodies of some 30 victims.
Twenty nine people wounded in the attacks remained in hospital, eight still in intensive care.
Many have had to undergo multiple surgeries due to complicated gunshot wounds. The gunman used semi-automatic AR-15 rifles, with large magazines, and shotguns.
Ardern has vowed to change gun laws in the wake of the attack, possibly banning semi-automatic weapons. An announcement will be made before the next cabinet meeting on Monday.
The gunman broadcast his attack live on Facebook and it was quickly distributed to other platforms, prompting Ardern and others to rebuke technology companies and call for greater efforts to stop violence and extremist views being aired on social media.