A Kiwi drug researcher says the discovery of fentanyl in New Zealand is a real concern and even being a "few grains" of salt off in dose size could kill.

The comments come after police revealed an investigation was under way after 12 people were hospitalised in Wairarapa over 48 hours following the drug being sold as methamphetamine or cocaine.

This is the first time powdered fentanyl has been found in New Zealand.

Associate professor at Massey University's SHORE & Whariki Research Centre Chris Wilkins said just a "line of powder" could be well-over the amount that could cause an overdose, even for an experienced drug user.

"The real issue here is that because it's concentrated, and so potent, people only have to make a small mistake in terms of dosing and they end up overdosing, we're talking about a few grains of salt difference could end up killing somebody."

Wilkins believed the potential for New Zealand to face the same opioid issues as the US was a concern, saying there is a "fairly large" opioid using population here.

Fentanyl, he said, was similar to morphine and heroin but it's much more potent, about 50 to 100 times so.

Detective inspector Blair MacDonald, Manager National Drug Intelligence Bureau, said one gram of pure powdered fentanyl is the equivalent of 20,000 safe doses of the drug.

Wilkins told the Herald fentanyl had played a key part in the opioid crisis in the US, including in the number of deaths from overdoses.

"The number of overdoses related to things like fentanyl and synthetic opioids went from around 3000 in 2013 to 30,000 by 2018."

As well as this, Wilkins said we have a large methamphetamine-using population and fentanyl could be made to look physically similar to P.

One of the reasons he told the Herald the synthetic opioid emerged in the US was because it is much more potent, cheaper and easier to conceal.

So, he said, your average heroin drug dealer can import fentanyl for as little as 50 times less for the same amount of product and they can sell it for the same price.

"It is used in the health system for particular types of really serious high-level pain so fentanyl is not a new drug, it's been around in the health system for quite a long time... There is a chance this was diverted from the health system."

However, he said illegal labs in China have also been identified as fentanyl sources and they have sites online where it is available.

"New Zealand has connections in the illegal drug market with China through methamphetamine so there is a chance that someone has imported quite a big batch of fentanyl and are now trying to sell it as counterfeit either morphine or heroin or even methamphetamine."

While there is an economic rationale for drug dealers, he said over time fentanyl gets adopted as the preferred opioid and this has occurred in the United States and Canada.

"Given how overwhelmed the health system is at the moment, particularly ambulances that might need to be the immediate response and the danger is that that's not going to be coming in fast enough."

The white powder which was used over the weekend had a very similar appearance to cocaine and authorities are warning it should not be consumed in any amount.

Given the risks, Wilkins said we need to figure out whether this is just an outlier, potentially taken from the medical industry, or something more serious.

"The real risk here is that we have a large batch of fentanyl that drug dealers are now using to counterfeit or to fill out heroin, or morphine or methamphetamine and that will mean fentanyl will get circulated quite widely without people knowing.

"People have really described fentanyl as probably the biggest risk drug since the emergence of heroin on the street."

He advised that drug users were able to use fentanyl test patches as one way of ensuring it isn't in their substances.

Anonymous reports of the drug can be made through High Alert's reporting system for unusual effects using the alert ID N22/029.