Senior Constable Bruce Miller, who regularly patrols the central city, said the criminal fraternity were well aware of the increased traffic in the festive season and effectively used it to do their own "shopping".
While looking through the Tiffin park yesterday he pointed out the sort of thing thieves went looking for.
A car, parked toward the rear and less exposed part of the park, had a reflective blanket spread over a large pile of property in the back seat.
"Not much use trying to hide it - that's just telling a thief there's something to break into for."
He often came across cars where property was openly in view and said thieves could smash their way in, grab whatever they could and then make off, in a matter of seconds.
"Everyone needs to be extremely vigilant about making sure their car doors and windows are locked and that any valuable items are kept out of view," Mr Sloane said.
"If you leave anything of value lying around that can be seen through a car window, you are just asking for trouble."
He said owners should take everything of value out of the car as sometimes putting things in the glovebox or boot was not enough.
"Thieves know where to look so that's not always foolproof."
Mr Sloane said despite constant warnings items like cellphones, wallets, handbags, laptops, cameras, iPods and even money was being reported stolen from cars in the city over the past couple of weeks.
Both the police and Napier City Council were moving to try to stem the spike. Mr Sloane said foot patrols would be increased while the council would be putting up security awareness signs at frequently targeted areas.
While there is no designated security camera system at the Tiffin park, that was set to change.
Council chief executive Wayne Jack said a project to install security cameras at the city's main parking areas was now under way. Cameras had been installed at the Marine Parade park and were now operational, he said.
"Based on the success of this installation further installs are likely - including a system at the Tiffin multilevel carpark."
Mr Sloane said word from the public about suspicious behaviour was vital to police.
"If you see anyone acting suspiciously around vehicles, in parks or around buildings, call police immediately. We need to know where these people are and we would rather respond to a call than not know about it - if someone is acting suspiciously chances are they are probably up to no good."