More than a dozen counterfeit $50 notes have been picked up by Manawatu Police in the last few weeks, and it's uncertain how many more are currently in circulation.
Stephen Gordon, the Reserve Bank's Head of Currency, Property and Security, sat down with Seven Sharp's Andrew Hallberg to explain how you can tell the difference between a fake note and a real one.
"If you look at the window, you'll see that the detail or the New Zealand map - of the denomination number, of the fern - they're simply not there. [Counterfeits] are essentially a bit of sellotape with three letters, so it looks starkly different to an authentic note so that's the first pick up there," Mr Gordon said.
In New Zealand, around one in a million is a fake note, compared with one in 10,000 in the United States, and one in 23,000 in Europe.
"In New Zealand, we're fortunate. Our counterfeit rate is very low by international standards. A lot of that is because we invest in and continually monitor our banknotes and upgrade them as required."
The most common target for fraudsters are busy supermarkets and petrol stations, where cashiers don't have the time to check its validity.
"The holographic window, there's a patch in there which is very complex, very hard to replicate on a counterfeit note, so there's that. There's the roll bar on the bird if you tilt the note.
"There's also the feel of the note. Our notes are made from a product called polymer, which is like a plastic which feels quite different to paper. Most counterfeits, or all counterfeits we see in New Zealand, are paper, so if you actually feel the note, it feels quite different to a counterfeit note. And the puzzle number, if you look at that in light - you'll see a complete number on a counterfeit note. Typically, you will not see that when you hold it up to the light [with fake notes]."
Mr Gordon says the counterfeits circulating in the Manawatu are easy to tell apart.
"Other things that are quite noticeable is there is a roll bar, so if you actually tilt the note, you get a colour bar roll across the bird. Typically, counterfeit notes aren't as sophisticated to replicate that, so if you do the tilt on a counterfeit note, you'll see no colour, roll bar, at all."
If you do come across a counterfeit note, Mr Gordon says "If you can avoid receiving it, don't accept it".
"Clearly, safety is paramount and you may not be in the position where you can refuse the note. If you do take the note, obviously put it to one side and contact the local police."