The number of July deaths blamed on a deadly batch of synthetic cannabis has risen to 10, as the drug continues to cause carnage in Auckland.

The body of 47-year-old man was discovered in a central city hostel on July 28. Acting Auckland Central Police Area Commander Matthew Srhoj said a possible synthetic cannabis link was being investigated.

Nine other people died in July as a suspected result of smoking synthetics, which are made from plant material sprayed with chemicals that mimic natural cannabinoids. But police said there was anecdotal evidence new batches of synthetics may contain weedkiller, fly spray or even rat poison.

The Chief Coroner says agencies are working hard to identify the chemicals responsible for the spate of deaths and hospitalisations, most of which happened in Auckland.

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Coroner, Judge Deborah Marshall, said an Auckland coroner raised the alarm on July 20 after seeing a number of synthetic-related deaths that week. 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.

By then, seven people had died after smoking the drug since the start of July.

West Auckland teenager Devonte Pierce was among those who died in July after smoking synthetics. Friends told media the 17-year-old had only recently begun using the drugs, and that they were easier to buy than marijuana.

Marshall said it was "imperative that the public were warned as soon as possible" and she and police issued a public statement saying seven people had died.

Auckland District Health Board and St John also warned up to 20 users were being hospitalised each day, with symptoms including psychosis and life-threatening seizures.

But the carnage continued. On July 26 a 24-year-old Papakura man died in Middlemore Hospital, and the following day a 31-year-old woman was found dead at a Kelston house, both after using synthetics. The death on July 28 at a central Auckland hostel brought the total to 10.

The exact causes of death have not been determined and all 10 cases have been referred to the coroner.

Marshall met with Associate Health Minister Peter Dunne in Auckland on Tuesday to discuss the after he claimed police were keeping the killer drug ingredients a secret.

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

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

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.

Coroner Morag McDowell would be in charge of investigating all 10 cases.