Police Commissioner Mike Bush has announced the process of identifiying all 50 victims has been complete and next of kin have been advised.

Watch Police Commissioner Mike Bush:

He said authorities were working hard to open up the Linwood mosque and Al Noor mosque in Christchurch where the shootings of worshippers took place.

In light of Prime Minister Jacinda Ardern's announcement of the banning of all military-style semi-automatic firearms and assault rifles, Mr Bush said there would be a grace period for those in possession of these.

"We'll be working with everyone to take those firearms off them and into a place of safekeeping," he told media this afternoon.

"The first step is to do it voluntarily, we'll then be working to ascertain if they haven't complied and those people will be in all likelihood prosecuted," Mr Bush said.

There were about 250,000 firearm holders in New Zealand, he said. People wishing to surrender their firearms must first contact police - either online or by phoning at 0800 311 311.

Referring to CCTV footage of the mosque attacks, Mr Bush said: I've seen that footage. It's really disturbing. I don't think that kind of thing should be in the public domain."

He said police were still in a state of high alert across the country.

Photo: RNZ / Ana Tovey

The criminal investigation into the Christchurch terror attacks is the largest one ever undertaken by New Zealand police.

The accused person who is now in custody was arrested within 21 minutes of the two attacks that killed 50 people at Al Noor and Linwood mosques, police said.

Earlier Mr Bush said that police strongly believed that the accused was on his way to a further attack when he was apprehended.