Warning: Contains footage of firearms. Simon Lusk explains the differences between a range of semi-automatic guns.

Prime Minister Jacinda Ardern oversaw recent changes which meant gun licence holders did not need to visit police stations when applying for permits for assault rifles, but could instead apply online.

Previously under the Arms Act, if someone wanted to become a gun dealer, get a firearms licence, import a restricted weapon, or get a permit to buy a MSSA [military style semi-automatic], they had to physically deliver an application to their nearest police station.

For example, if someone with an E-category endorsement was buying an MSSA, they would have to visit their police station for a permit, show the permit to the seller, and then take the weapon back to police.

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Under the changes, which came in just before Christmas, that process could be done online, and the firearm shown by video call. Police could ask to see the weapon in person if they were not satisfied they had identified it.

A critic of the change, firearms lawyer Nicholas Taylor, said: "It's been done for all the wrong reasons - this is exactly an example of the type of problem that's caused this event [in Christchurch]."

He described it as "crazy" as it meant less face-to-face contact between the applicant and police.

The Prime Minister's office says the changes were designed to allow for paperwork to be done electronically and didn't remove the requirement for face-to-face vetting when someone applied for a firearms licence before applying for access to an MSSA.

The accused gunman got his New Zealand firearms licence in November, 2017 and began buying weapons soon after, including online from Gun City in Christchurch.

Ardern was the chair of an executive committee which ushered through changes to arms regulations.

Ardern announced changes to firearms law on Thursday which include a ban on MSSAs and accessories which can convert a standard semi-automatic into an MSSA.

She has described our guns laws as a "blueprint [for] what not to do".

GETTY IMAGES Jacinda Ardern presided over changes to firearms regulations in December.

The changes in December were made by a mechanism known as an order in council, where regulations are amended without the need for an Act of Parliament.

"Cabinet sought advice and was told that the amendments would not change the strength or rigour of the vetting process. It simply provides an alternative option for the filing of paperwork," the PM's office said.

A Government source said the Christchurch mosque shooter was able to convert guns bought on a standard licence to MSSAs, so even if the online option was available at the time it wouldn't have been relevant in his case.

Taylor said the changes had already come into effect but there had been no public announcement.

"Really no-one knew about it at all.

Anatoly Vartanov Permits for military style weapons can be applied for online after changes made in December.

"I heard from a dealer who phoned up, he was told by local arms officers in Auckland that permits to procure restricted weapons like MSSAs and pistols...now aren't being dealt with by the local arms office - they all have to go to Wellington.

"That would have been unlawful before the change [in December] because it's specified in the Act that an application for a restricted weapon...has to be done at your local arms office."

Taylor said applying in person allowed police to assess someone.

"Quite often I had police officers saying 'your client came in to see me and he was aggro and...saying strange things and acting weirdly'.

"So you're actually missing out on that very vital step."

It's understood the changes were part of a police move to centralise firearms vetting.

Police arms officers were told in January they would be restructured, with 76 district-based positions disestablished and 280 casual vetting staff positions cut entirely.

They would be replaced by 36 field-based positions and 47 centralised positions at a facility in Kapiti.

Firearms groups were furious, saying there had been little consultation.

It's unclear how the events in Christchurch will impact on the changes.

Acting Superintendent Mike McIlraith said "any final decision will reflect Government intent".

He said police had reviewed their administration of the Arms Act because it was more than 30 years old and had been "very paper-based, manual and at times inconsistent across districts".

Firearms staff and the community were consulted, he said.

"They told us we need to make changes."

McIlraith said the new system would allow people to access police arms services wherever they were needed, with support online.

"Police want a structure focused on both improving our service and ensuring it is aligned to our mission to be the safest country."

National's police spokesperson, Chris Bishop, said he understood the proposed restructuring had been dumped even before events in Christchurch, but police were denying that.

Bishop has faced criticism for posting a photo of himself on Facebook celebrating the "victory" of having the policy dropped.

He said centralised vetting was a retrograde step and would impact on public safety.

"Arms officers and vettors are a really important part of the system and we were really concerned.

"That proposal came out of nowhere - the licensed firearms community felt really blindsided by it.

"The reality is that at 1.40pm on Friday everything changed and we're now going to have to have a good look at the whole system."

Clarification: This story has been updated to make it clearer that, despite the change, anyone who wanted access to an MSSA still needed to meet face-to-face with police when applying for their original firearms licence.

Chris Skelton Firearms law specialist Nicholas Taylor says the changes were "crazy".