It's becoming "far too common" for young people to use starter pistols or imitation firearms to carry out a crime, the police union says. 

Many victims - and police officers - cannot tell if a firearm is real or not, so using an imitation weapon can have serious consequences, Police Association president Chris Cahill said. 

"We certainly hear about imitation firearms...being used in armed robberies. 

"Certainly the person who is the victim of that has no real way of knowing if it's a real firearm or not so it has a traumatic effect on them." 

He said starter pistols are not covered by the Arms Act so anyone can buy one, and they are reasonably priced, which raises questions over their availability to young people. 

A woman, 20, was arrested and charged yesterday after she allegedly pointed a starter pistol at another woman's head during a fight between Auckland school students in Ōtāhuhu. 

A video of the brawl, that circulated on social media, appears to show the young woman shouting expletives at her victim before brandishing the alleged fake gun. 

"I was very alarmed about that incident," said Cahill. 

"What alarmed me the most was the casual manner in which the offender with an imitation firearm behaved. It was like there was no second thought about pulling the gun out and presenting it to someone. 

"To me, it's pretty scary." 

The woman appeared in Manukau District Court today charged with threatening to cause grievous bodily harm and carrying an imitation firearm with criminal intent. 

Police said the incident allegedly involved a starter pistol which has now been handed in. 

"What worries me is that younger people are trying to replicate what they're seeing older offenders doing," said Cahill. 

She is one of a string of young people across Auckland facing charges for possessing either imitation or modified pistols. 

Charging documents filed in District Court in recent months indicate that the weapons are common among younger criminals. 

Yesterday a man, 20, was charged for carrying an imitation firearm, namely a black pistol, in Ōtāhuhu on Sunday. 

Earlier this month two men in their 20s were charged on Auckland's North Shore for being in possession of two converted starter pistols. 

"It's far too common," said Cahill. 

"What you're seeing in those court records is exactly what our members are telling us out on the street, and it's probably the age level that's changing. 

"The lower age level of people carrying them is the biggest concern." 

He said starter pistols are affordable and appear easy to obtain online, and so the accessibility of starter pistols needs to be "looked at". 

"There are very few legitimate reasons for them anymore." 

A police source told the Herald it was concerning that criminals are buying starter pistols online, and with some very small, cheap and easy modifications they can be transformed into a weapon that can fire .22 ammo. 

"You don't need a licence to buy a started pistol because it's a blank but it's so easy to configure them." 

Cahill said a firearms licence should be required to purchase a starter pistol and they should fall under the firearms registry. 

"If people have a legitimate reason for it, they will get a firearms licence. If they don't, they won't be able to get them as easy."