The Chief Coroner says agencies are working hard to identify the chemicals responsible for a spate of deaths and hospitalisations among synthetic cannabis users.

The coroner, Judge Deborah Marshall, met with Associate Health Minister Peter Dunne in Auckland today to discuss what was in the killer drugs.

Her statement came as police announced July's death toll may have risen to 10, after a 47-year-old man died in a central Auckland hostel due to suspected synthetic cannabis use.

Nine other people died in July as a suspected result of smoking synthetics, with police saying there was anecdotal evidence they may contain weedkiller, fly spray or even rat poison.

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"I share Mr Dunne's concern at the suffering synthetic cannabis and other illegal drugs are causing to the wider community," Marshall said.

"I also share his view of ensuring the public has as much information as possible about dangers of drug use."

The Chief Coroner said on July 20 an Auckland coroner raised the alarm after noticing a number of deaths that week while on duty. Inquiries found several more people had died in the previous two weeks after smoking the drugs.

The next day St John's medical director also contacted her to raise concerns about how many people were being taken to hospital under the influence of synthetics. Another death had been reported overnight.

Marshall said it was "imperative that the public were warned as soon as possible" and she and police issued a public statement later that day. Auckland District Health Board and St John also sent out a statement.

The coroner's office, the Ministry of Health, police, district health boards, Environmental Science and Research and pathologists are working to identify the substances involved, Marshall said today. Coroners will provide updates.

The exact causes of death have not been determined. All the cases have been assigned to one coroner, Morag McDowell, to ensure she has all the available information and can liaise with other agencies.