Hundreds of police patrol cars are out on the job at any one time without firearms.
Figures obtained by RNZ show while there are 1521 police cars with room to carry gun safes, there are only 1109 of the security cabinets to go around - and the Police Association says that has to change.
A routine checkpoint on Te Atatu Road in west Auckland for police in October quickly turned into a high-speed police chase when a car failed to stop.
The police said a 23-year-old woman shot at officers from the car's window and then fired again before colliding with a pursuing police vehicle.
When the car crashed, the driver got out and - according to police - fired at officers with a sawn-off shotgun, before both of them fled on foot.
Police Association president Greg O'Connor said there were no firearms in either of the officers' vehicles during the incident.
He said it was one of several high-profile cases in recent months where officers have been caught out unarmed when confronted by people with guns.
"Our first-line response vehicles do have firearms and they would be the vehicles normally sent to any incidents.
"However, there are what we call second-tier vehicles, who are out there doing police work, who either stumble across incidents or are the nearest when an emergency occurs.
"It's not uncommon for police vehicles to turn up when there is no firearm in the vehicle."
Superintendent Chris Scahill, from Police National Headquarters, said in a statement not all cars were fitted with gun safes because not all of them were frontline response vehicles and not all officers were trained to use guns.
There were 200 more of the security cabinets than there used to be, he said.
Mr O'Connor said every police officer who was likely to encounter an armed offender as part of their day-to-day duties should have sufficient training and access to firearms.
"While we accept there appears to be no political will for general arming, the quid pro quo for that should be that every vehicle has firearms available should they be required.
"And I believe the public generally think that's the case when in reality it is not."
Mr Scahill said the police were continuing to work with each district to ensure they were equipped to respond to armed threats.