The deaths of at least seven people in Auckland this month have been linked to the use of synthetic cannabis, according to police.
The Chief Coroner and police have issued a warning, saying there have been seven cases where the deceased is believed to have used synthetic cannabis recently or were found with the drug on them.
Chief Coroner Judge Deborah Marshall said she had been advised by St John Ambulance that there had also been a "significant" number of non-fatal cases where people have been hospitalised after using the drug.
"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," said Judge Marshall.
Police said the issue was not unique to Auckland, and they were also concerned by the impact of synthetic cannabis in other communities around the country.
Detective Inspector Gary Lendrum said police were seizing it every day, with children as young as 13 found high on it just last week.
"I don't know why there has been a spike in deaths, clearly there is something occurring. What we do know ,anecdotal evidence suggests synthetic cannabis, which is dangerous enough in itself, is being laced with chemicals. And whether that is causing the deaths, I don't know."
Mr Lendrum said more people would die unless something was done, and the police needed the public's help finding those selling it.
Synthetic cannabis was banned when the Psychoactive Substances Amendment Act came into effect in May 2014.
Police have also released video of an incident in Auckland's CBD earlier this year where a male was violently ill and could barely stand after smoking synthetic cannabis: