CAR thefts in Whanganui have increased 25 per cent in the past four years - and police are solving a lower percentage of them.
Figures released to the Wanganui Chronicle show 206 vehicles were stolen in Whanganui last year, part of an annual increase in thefts in each of the past four years.
However, vehicle thefts were less likely to be solved - the resolution rate dropping from 23 per cent in 2014 to 16 per cent last year.
That means five out of every six cases did not result in an offender being caught.
Labour's police spokesman Stuart Nash said the resolution rate showed police were underfunded, and were forced to prioritise other areas at the expense of investigating thefts and burglaries.
"The police themselves - certainly the frontline officers - do a fantastic job. But that thin blue line is really, really stretched," Mr Nash said.
"We just can't continue like this - when burglaries and car thefts aren't getting solved and the public is losing confidence in the police's ability to do the basics."
Nationwide, the number of recorded vehicle thefts rose to 20,646 last year, a 12 per cent increase on 2014, and a 20 per cent increase since 2012.
"Burglars know they've got a 90 per cent chance of getting away with it. I don't think they rationalise it like that, but that's the reality - they've got a 10 per cent chance of getting caught," Mr Nash said.
The national resolution rate was 11.6 per cent, and thieves got away with taking more than 50 cars a day.
In a written response to the Chronicle, police acting assistant commissioner Dave Trappitt said low resolution rates for crimes such as burglary and vehicle theft were because cases were "difficult to resolve" and were often reported hours after the crime occurred.
He said an increase in vehicle ownership may also be a factor behind the increase in thefts. Police recognised the impact of vehicle crime on victims and "will continue to prioritise this as appropriate".
AA Insurance (AAI) spokesman Aaron Dickinson said thefts had increased nationwide but the number of theft claims received remained stable.
He said less than 1 per cent of vehicles insured by AAI were stolen each year.
The majority of these were cars more than 10 years old, he said.
Mr Dickinson said car owners should not assume their vehicle wouldn't be stolen and they should always ensure a car was as difficult as possible to steal.
"Thieves will always go for the easiest, fastest option.
"So if you make it just a little bit harder for them, then chances are they'll move on to an easier target."
Mr Dickinson said theft had not contributed significantly to insurance premium costs.