Drug pushers are adding life-threatening toxic chemicals such as weedkiller and fly spray to synthetic cannabis, say police.
Seven people have died in the last month from using the drug, following a surge in its use.
Avondale Police area prevention manager Acting Inspector Marcia Murray said many users did not realise the toxic chemical cocktail they were smoking.
She said there had been a "concerning" rise in synthetic cannabis use.
"All of these appear to be manufactured privately by people.
"Any drugs that we seize, we get them tested. What comes back are the technical aspects, which show things like fly spray and weedkiller.
"The most concerning thing is I wonder whether people realise what they're putting into their bodies, and the fact that it is extremely dangerous.
"They're putting their lives at risk.
Murray said police wanted to hear from anyone with information about those dealing the drug, so they could shut them down.
Emergency services in Auckland are frequently busy with synthetic cannabis-related jobs.
At 4.30pm today a frustrated parent called police and ambulance officers to remove their son and two others who had been smoking synthetic cannabis on their property in Ranui.
Fifteen minutes later police were called to keep St John paramedics safe as they dealt with a person who had been using synthethic cannabis near the Civic Building on Queen St.
Wellington emergency medicine specialist Dr Paul Quigley said Hutt Valley Hospital was regularly having to treat users of synthetic cannabis.
He said a single smoke of synthetic cannabis was equivalent to 15 normal joints.
"Synthetic cannabis is one of the more dangerous products around and is responsible for some immediate health harms."
He said the drugs could cause epileptic seizures, heart palpitations, kidney problems, significant anxiety, insomnia, and worsen mental health conditions until they reached the level of psychosis.
"Because synthetic cannabis is so much more potent than natural cannabis we were also seeing the effects related to substance abuse and addiction developing rapidly," Quigley said.
"Users would need to smoke regularly every 3-4 hours, even waking during the night to smoke."
Middlemore emergency medicine consultant and toxicology expert Dr Chip Gresham said there seemed to be a new synthetic cannabis strain that was making people "very sick".
"It is critical that people understand that even if they have used it many times in the past, this new brand or new batch can be life-threatening."
Gresham said if someone smoked synthetics and began to feel strange or unwell, they needed to urgently seek medical help.
While users of the drug are putting themselves in danger, others point out the harm to the rest of the community.
Retailers and business owners in Auckland's CBD say the spike in synthetic cannabis use is creating a threatening atmosphere.
Robert Jones Holdings New Zealand general manager Greg Loveridge said in the past six months problems with drugs, antisocial behaviour, and begging on Queen St had risen sharply.
His company owned two buildings on Queen St, and was scrambling to respond to frightening behaviour that had left staff feeling unsafe.
"The female staff don't feel safe on the street, visiting executives from overseas don't feel safe walking back to their hotel after dinner.
"People have managed to get into the building and gone to sleep in the meeting rooms. I've had people try to harass my staff.
"Our retailers have told us they've seen clear drug dealing, the exchange of money in the street, but the police are doing nothing about it.
Staff and shop workers have been verbally abused or physically threatened.
"Just this weekend, we had staff feeling unsafe in a shop," Loveridge said.
"The shop assistant was confronted by a man on drugs who walked in off the street, and made aggressive movements towards her and was yelling at her.
"I've seen people urinating in the streets.
"[Drug use] was happening outside our building just the other day, a very rough group of older men.
Loveridge said police numbers and resources needed a boost, so they could crack down on the issue.
Alcohol and Drug Helpline 0800 787 797