They had noticed some slightly different symptoms compared with last year.
Whatever the latest batch was, it was deadly and violent, he said.
"Predominantly last year we were seeing a lot of patients with seizures or convulsions and this year we're seeing very little of that. So we think something about the mixture of chemicals has changed between last year and this year.
"Most commonly patients become unconscious. They often have very poor breathing. And as they regain consciousness, it's common for them to appear very confused, agitated and often violent. Between people but also potentially violent towards our own staff."
He knew of two deaths in just the past few weeks in Auckland.
"[They] can't yet be proven to be related to synthetic cannabis but they occurred shortly after smoking a substance that was thought to be synthetic cannabis."
Those deaths were being reviewed by the coroner.
The police are also worried about the spike.
Detective Inspector Scott Beard told the Herald police were continuing to target suppliers and had made recent arrests, including at the weekend.
"If people have got information about who's manufacturing, who's importing, who's dealing … police want to know."
Under the current law, manufacturing or possessing psychoactive substances for sale and supply carries a maximum sentence of two years in prison.
A bill to raise the maximum penalty to eight years passed its first reading in Parliament in March with the support of National and NZ First.
This would bring the maximum sentence into line with supplying a Class-C drug, such as cannabis.
The bill has the support of the parents of 22-year-old West Aucklander Calum Jones, who after promising his sister he wouldn't take synthetic drugs, was found lifeless on the floor hours later in September last year.
His parents spoke out at the time in a bid to put pressure on the Government to do more to help struggling addicts and to support their families.
And a coroner's inquest in Taupō today heard evidence relating to the death of 49-year-old synthetic drug user Andrew Brian McAllister, who died in August last year.
McAllister collapsed at a Taupō home. He went into heart arrhythmia, stopped breathing and the flow of blood to his brain ceased, eventually causing an irrecoverable brain injury, the inquest heard.
It was the first inquest into a spate of deaths across the country last year blamed on a stronger-than-usual batch of synthetic drugs.
The inquest heard that synthetic drugs are 85 times more potent than natural cannabis.
The coroner reserved his decision.
