Police have issued a stark warning after the deaths of at least seven synthetic cannabis users in Auckland over the past month.

"If we don't do something about this, further people are going to die," Detective Inspector Gary Lendrum said at a press conference on Friday afternoon.

"We've got reports of 13-year-olds right through to 64-year-olds using this product, so it's right across New Zealand, and right across society."

FILE IMAGE/STUFF Synthetic cannabis is a banned substance in New Zealand, and can be much stronger than the organic variety.

Lendrum said synthetic cannabis had been a problem for some time, but there had been a sudden unexplained spike in recent months.

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"There is clear evidence that it's being distributed by gangs. Where it's being manufactured, and how, is less clear," he said.

The deaths were confirmed in a joint statement released on Friday that included a further warning from Chief Coroner Judge Deborah Marshall.

"I've also been advised by St John that there have been a significant number of non-fatal cases where people have been hospitalised after using the drug, which is known to cause potentially fatal seizures," she said.

"While the police and coronial investigations are still at an early stage, and the final causes of death have yet to be established, the number of cases where synthetic cannabis appear to have been a contributing factor has prompted me to issue this public warning."

Police also released CCTV footage of an incident in Auckland's CBD earlier this year that shows a man becoming violently ill after smoking synthetic cannabis.

"We have grave concerns as users don't know what poisonous chemicals they are potentially putting into their bodies when they're smoking this drug," Lendrum said.

He urged users of synthetic cannabis to stop immediately, and called on their family members to intervene.

"Please contact us if you're aware of people in your community selling this drug," he said.

Police have taken a strong stance against synthetic cannabis, with one operation in Avondale resulting in 12 arrests over the past few months.

"It is a dangerous, illegal substance and we will arrest those who are selling this harmful drug and place them before the courts," Lendrum said.

Synthetic cannabis can be much stronger than organic cannabis, and is an illegal substance in New Zealand.

Legal highs were permitted here until May 2014, when they were banned unless they could pass a strict testing regime to show they were safe.

Associate Health Minister Peter Dunne has said there was a stockpiling of legal highs in 2014 before the ban came into effect.

Synthetic cannabis use is relatively uncommon in New Zealand, with usage rates about one third of the global average of 1.1 per cent, according to the latest Global Drug Survey.

An earlier study of legal high users in Auckland in 2016 found about half of those using synthetic cannabis were considered dependent on the product.

"It was surprising how many users were daily or more frequent users, so clearly synthetic cannabis is associated with pretty frequent use," researcher Dr Chris Wilkins said at the time.

"The other finding was that synthetic cannabis was associated with some health harms, so we've got to be aware of that."

Adverse effects most commonly reported from synthetic cannabis use were: trouble sleeping (29 per cent); vomiting/nausea (25 per cent); short temper/agitation (21 per cent); anxiety (21 per cent); strange thoughts (16 per cent); and heart palpitations (14 per cent).

'GROSSLY DISTURBED BEHAVIOUR'

St John ambulance and the Auckland District Health Board (DHB) said in a joint statement they were seeing a "rapid rise" in patients suffering the effects of drugs, thought to be synthetic cannabis, in the Auckland area.

St John medical director Tony Smith said ambulance officers had responded to 23 synthetic cannabis incidents on Thursday – an all-time high – and 20 on Wednesday.

"Patients under the influence of this drug are exhibiting grossly disturbed behaviour, suffering seizures," he said.

"Most concerning is that the drug appears to be linked to some people's hearts stopping beating and we have had seen seven sudden and unexpected deaths.

"In some instances their hearts have just stopped from a massive cardiac arrest."

Patients who were "lucky enough to wake up" could exhibit abusive and threatening behaviour and be "very difficult" to manage, Smith said.

Dr Margaret Wilsher, the chief medical officer for the Auckland DHB, said Auckland City Hospital had seen a rapid increase in patients who had used synthetic cannabis.

There had been 22 cases and one death at the hospital over the past five days.

"The presentation features are often dramatic, including agitation, psychosis, an increased heart rate, seizures, and sometimes collapse."

Most of the cases were occurring in central Auckland, but ambulance officers were also seeing incidents across the greater metropolitan area.

Patients being seen ranged in age from teenagers through to the middle-aged, Wilsher said.​

Labour leader Andrew Little said the reports were "incredibly disturbing".

"I know police are saying they're going to conduct an investigation – the Minister of Health has got to be involved in that. We've got to understand what's happened there.

"It throws open the whole issue about the ability to regulate in this area and people's safety with a substance that is constantly changing. It may well be time, even though it's been a reasonably short period of time, for Parliament to review and revisit just what it has done in relation to synthetic cannabis."

'NOT AN ISSUE UNIQUE TO AUCKLAND'

Police said they were also concerned at the impact of synthetic cannabis in other communities in New Zealand.

"This is not an issue unique to Auckland," they said on Friday.

Dr Paul Quigley, emergency medicine specialist at Wellington Hospital, said it appeared illicit use of synthetic cannabis was becoming a particular problem for those from lower socio-economic groups.

"Synthetic cannabis is one of the more dangerous products around and is responsible for some immediate health harms," he said.

"Even a single smoke of synthetic is the equivalent of up to 15 normal joints."

Few, if any, synthetic cannabis users were seen at Wellington ED, but Hutt Valley Hospital saw users regularly, Quigley said.

As synthetic cannabis was so potent, doctors saw effects related to substance abuse and addiction developing rapidly, he said.

"Users would need to smoke regularly every 3-4 hours, even waking during the night to smoke, and would exhibit signs of withdrawal on cessation."

David Richards, Canterbury DHB's emergency department clinical director, said the ED was seeing people "on a regular basis" suffering from the ill-effects of both synthetic and non-synthetic cannabis.

Numbers were increasing slightly, he said.

"Anecdotally, it's been noted there is a small change in the side effect profile of the synthetic drug in some people that could indicate there is a new substance, or new ingredient, around.

"Some people are showing increased agitation and confusion, and a few people have suffered seizures."

Christchurch Detective Inspector Greg Murton said officers were dealing with the effects of synthetic cannabis on an ongoing basis.

"In our view synthetic cannabis is as harmful . . . as many other drugs simply because of their chemical makeup. They're not actually cannabis, they're chemicals sprayed on plant material."

The drugs were "very prevalent" in Christchurch, he said.

In 2016, a Stuff investigation found a web of people selling synthetic cannabis online via social media.

A low-level street dealer who sold the drug to a reporter as part of the investigation said he earned at least $1000 a week from supplying to addicts.

That same year, police exposed a group which was allegedly dealing millions of dollars worth of synthetic cannabis in Christchurch.

The investigation – dubbed Operation Sin – included the seizure of 173kg of the drug and was the largest of its kind in New Zealand.