The number of guns seized in New Zealand is significantly under-reported, making it difficult to assess the extent of firearms use, the Police Association says.
Its president, Greg O'Connor, said official police statistics had long failed to reflect what front-line officers had said about the numbers of guns they saw in their day-to-day work.
"One of the frustrations that we felt as an association was that our members on the ground on the street were telling us about how many firearms they were seizing, how many they were stumbling across, how many offenders they were dealing with who have access to firearms - but the statistics kept by police headquarters didn't corroborate that," he said.
He said in one instance, association members recorded 52 firearm seizures over a six-week period, but said that was significantly lower than the figures police recorded in their database.
A police spokesperson confirmed that 129 firearms seizures were recorded during that time period, of which 52 were voluntarily notified to the Police Association by its members.
In a statement, they said police acknowledged that there may be some under-reporting of firearms seizures.
"Police currently use a number of systems to record this information, which may lead to discrepancies in the information which is held. To address this, police is currently reviewing the relevant processes to ensure all information about seized firearms is captured."
Mr O'Connor said officers were confused about where to file reports, and there was no centralised way of collecting them from around the country.
"One of the issues is that there are different methods of recording the seizing of firearms and they're not well understood by staff in the districts. In some cases it's collected by what we call a firearms surrender form, others it's just exhibited. The problem is there is no central collection."
That was in contrast to the way police recorded drug seizures, where officers must notify headquarters so there was a very accurate national record kept, he said.
Mr O'Connor said, in some districts, police were working to improve the reporting process when guns were found, but he wanted to see that happen across all districts.
It was crucial for police to have the right statistics.
"We know that unless you have statistics to back things up, then clearly the researching and strategies around it won't be employed."
The issue is currently before a select committee.
Parliament's Law and Order Select Committee is holding an inquiry into how, and from where, criminals are getting their hands on firearms.