New Zealand will ban military style semi-automatic and assault rifles under tough new gun laws following the killing of 50 people in the country's worst mass shooting, Prime Minister Jacinda Ardern said on Thursday.

Ardern said she expects the new laws to be in place by April 11 and buy-back scheme will be established for banned weapons.

"Now, six days after this attack, we are announcing a ban on all military style semi-automatics (MSSA) and assault rifles in New Zealand," Ardern said.

“Related parts used to convert these guns into MSSAs are also being banned, along with all high-capacity magazines."

A lone gunman armed with semi-automatic rifles including an AR-15, last Friday killed 50 people in two mosque attacks in Christchurch.

Australia banned semi-automatic weapons and launched a gun buy-back after the Port Arthur massacre in 1996 in which 35 people were gunned down.

The AR-15 was used at Port Arthur and has been used in a number of high-profile U.S. mass shootings.

"On 15 March our history changed forever. Now, our laws will too. We are announcing action today on behalf of all New Zealanders to strengthen our gun laws and make our country a safer place," Ardern said.

“All semi-automatic weapons used during the terrorist attack on Friday 15 March will be banned."

Ardern said that similar to Australia, the new gun laws will allow for strictly enforced exemptions for farmers to conduct pest control and animal welfare.

"I strongly believe that the vast majority of legitimate gun owners in New Zealand will understand that these moves are in the national interest, and will take these changes in their stride."

Federated Farmers, which represent thousands of farmers, said it supported the change.

"This will not be popular among some of our members but after a week of intense debate and careful consideration by our elected representatives and staff, we believe this is the only practicable solution," Federated Farmers Rural Security spokesman Miles Anderson said in a statement.

New Zealand, a country of less than 5 million people, has an estimated 1.2 to 1.5 million firearms, around 13,500 of them MSSA type weapons.

The minimum legal age to own a gun in New Zealand is currently 16, or 18 for military-style semi-automatic weapons.

MOSQUES TO REOPEN FOR FRIDAY PRAYERS

The bullet-riddled Al Noor mosque in Christchurch was being repaired, painted and cleaned ahead of Friday prayers, as grieving families buried more victims.

Ardern has 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 since the attacks. "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.

Australian Brenton Tarrant, 28, a suspected white supremacist who was 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 release to the families the bodies of some 30 victims.

Twenty nine people wounded in the attacks remained in hospital, eight still in intensive care.

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.