The new generation of body scanners are configured to generate genderless stick-figure images.

Kiwis will soon be showing off more than just their boarding pass and ID before they board a plane, with full body scanners coming to New Zealand airports from next year.

The Aviation Security Service plans to install advanced imaging technology (AIT) scanners at Auckland Airport's international terminal next year. Christchurch, Dunedin, Queenstown and Wellington airports will follow by late 2020.

It comes after a trial at Wellington Airport last year, which cost about $20,000.

But there are fears the scanners will create bottleneck queues at security screening points, with a report on the trial showing processing was slower for all passengers.

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The so-called "naked scanners" have been a feature in United States airports since 2010 after "underwear bomber" Umar Farouk Abdulmutallab​ tried to blow-up an international flight with plastic explosives.

ROHDE & SCHWARZ/SUPPLIED Full body scanners will be rolled out at international airports across the country.

The technology has been controversial because of privacy concerns, with critics describing them as a "digital strip-search".

Devices that produce an unclothed image of a person breach New Zealand's Aviation Crimes Act, so the scanners will be configured to reveal only a genderless stick figure image that highlights the areas of a passenger's body that require investigation by security staff.

Suspicious or foreign objects will also not be displayed – they will instead be indicated with a coloured marker.

The scanners use non-ionizing radiation, which has no proven adverse health effects.

Passing through the scanners won't be mandatory, but those who refuse will have to undergo a "pat-down" search.

There has been no increase in New Zealand's terror threat level. But documents released by the Aviation Security Service (Avsec) under the Official Information Act note the scanners "are becoming the norm" in international airports.

"Recent threats to aviation security have demonstrated an increase in people concealing prohibited items on or in their bodies, including Improvised Explosive Devices (IEDs)," chief executive Graeme Harris wrote to former Transport Minister Simon Bridges last year.

"Millimetre wave technology, such as that used in AIT machines, is able to detect the concealment of such items, even when they have no metal parts or power sources."

In a ministerial briefing, he also noted: "Global bodies, such as the International Civil Aviation Organization, the International Air Transport Association and the Airports Council International, are continuing to encourage evaluation and deployment of AIT systems."

Ben Smith, the Aviation Security Service's strategic development group manager, said in a statement to Stuff that maintaining the highest level of security for travellers was the driving force behind the decision to use full body scanners.

"As with any new technology, its initial introduction may lead to some delays for passengers early on. The trials helped demonstrate how these can be minimised and Avsec has sought to incorporate these ideas into the overall equipment design," he said.

"Avsec will also be working closely with airlines and airport companies to ensure passengers know what to expect, in a bid to further minimise impacts."

STEVE BIDDLE A trial of the body scanners in 2017 showed increased processing times for passengers.

He could not provide the costs of the technology rollout.

Council of Civil Liberties chairman Thomas Beagle said it was "overkill" but he was now "resigned to the over-securitization of the border."

"We acknowledge the need for security but think it is probably overdone. Air travel has got a lot less pleasant."

The trial report from Wellington Airport showed the average time to pass through walk-through metal detectors was 4.7 seconds, compared with 18.8 seconds for the AIT scanners.

But the report did note staff and passengers were unfamiliar with the equipment that slowed things up.

Increased staff levels would likely be needed to operate the new scanners, the report said. It also noted passengers were happy, saying the evidence suggested passengers saw the AIT technology as preferable to the current system.

JARRED WILLIAMSON/STUFF Auckland Airport will be the first in the country to get the new scanners.

"The majority of passengers reported an increased perception of safety, thought AIT was good for New Zealand and gave positive responses when comparing AIT to the usual screening method."

Wellington Airport spokesman Greg Thomas said Aviation Security were responsible for screening travellers.

"We provide effective facilities for the security screening to take place. We want to ensure a positive experience for travellers," he said.

"The airport community at Wellington works together to review queue times, and the airport encourages Avsec to take any appropriate steps to maintain an acceptable level of service whenever necessary."