Some vehicle owners are pretending their vehicles are ambulances to get hundreds of dollars off registrations.
Figures released by the Transport Agency suggest Otago, in particular, is overrun by so-called "Usage 6" vehicles, the catch-all category for non-commercial ambulances.
The figures show 230 such ambulances in Otago - but officialsbelieve the figure is wrong.
The Auckland region, which has about 10 times as many people as Otago, has 251 non-commercial ambulances, according to the agency's books. Wellington has 62.
Transport Agency media manager Andy Knackstedt said he believed there were only 40 genuine ambulances in Dunedin.
Most of the others on the list could be regular passenger vehicles, which were more expensive to register.
Mr Knackstedt was unsure why southern numbers were so high.
"I guess it comes down to people's willingness to falsely register their vehicles."
The difference between the registration prices is significant. The annual registration fee for non-commercial ambulances is $59.64, Mr Knackstedt said. It costs $287 to license a petrol-powered private car and $417 to license a private non-petrol car, the NZTA's schedule of fees shows.
Transport Registry Centre manager Brett Dooley said errant vehicle owners were in NZTA's sights.
"The Transport Agency monitors vehicles licensed in this category on a regular basis and will write to owners of vehicles licensed where their eligibility appears to be questionable," Mr Dooley said.
"On-road enforcement by police also plays an important role, as police are able to sight the vehicle and verify whether it is being used legitimately as an ambulance.
"Any person who knowingly provides false or misleading information is committing an offence and could be fined up to $1000."
