Hundreds of dollars of counterfeit notes have been palmed off in Waikato, with retailers being warned to keep a sharp eye out during the Christmas rush.
Since October, police say there have been seven incidents with alleged fake notes, including $50, $20 and $10 notes.
They have been reported across Waikato, including Hamilton East, Te Rapa, Frankton, Te Awamutu, Beerescourt, and Paeroa.
Waikato Prevention Manager Inspector Hywel Jones told Checkpoint in one case, a few real bills were mixed in with a total $750 of counterfeit banknotes.
"That was in early October. We've got CCTV and witness accounts for that and we are following positive lines of inquiry."
At this stage, police have not connected this case with the recent alleged use of counterfeit banknotes in the Pukekohe area, Jones said.
"Counterfeit notes have been around for many, many years as you know, and it would probably be more than one criminal group that are trying to use those."
Jones warned retailers and people to be aware of the fake notes.
"They're actually quite good [in resembling the real notes] from what I've seen. So, I would say be very careful when handling cash at the moment and, if [you have] any doubt, don't accept it and call police.
"If you're handed a number of notes, check each one basically. And like I said, if you spot it, after you accept it, just limit your handling so we've got maximum forensic opportunities.
"I suppose with this time of year, with the shopping season coming up, I'd expect to see an attempt to put some more into the market at that point."
There are some security features - which help distinguish fake notes - on the two types of banknotes in circulation at the moment.
"The first one has a bird at the lower left front. And if you move that back and forth, you should see a rolling bow of color, as it's tilted and you can hold it up to the light and you'll see a fern in the centre of the bird," Jones said.
"The second older style of banknote has got a small oval window at the front right and holding it up to a light will show a watermark of the queen to the left of that window.
"And finally, for those retailers, I suppose who've got a UV torch or black light, both styles have a patch that shows the denomination that glows which is located on the front left of the note."