Police raids around the country have recovered large quantities of "zombie" drugs with an estimated value of $1.5 million.
Police raided nine properties in Palmerston North, Auckland, North Canterbury and Christchurch as part of an operation codenamed Tiger.
Two more properties in Palmerston North were raided.
There have been 10 deaths thought to be related to synthetic drugs in recent weeks in the Auckland area.
Acting detective inspector Roger Small said more than 10kg of synthetic drugs were found overall.
Police also found four guns.
"This is only the tipping point,'' he said.
Mr Small said the investigation began in June after Customs intercepted AMB-Fubinaca and AB-Pinaca, psychoactive precursors used in the manufacture of synthetic drugs.
Customs intelligence manager Wei-Jiat Tan said border seizures were a good indication of new and emerging drugs.
"Chemical properties of psychoactive drugs are ever evolving and potentially lethal - especially if amateurs are producing them.
"These drugs can be life threatening for users, who have no way of knowing what they're really taking.''
Synthetic cannabis is made by treating plant-based material with the precursor compounds.
Raids followed searches by police in Waitematā last week, when 2kg of a synthetic precursor and 11kg of synthetic smokable drugs were uncovered.
The drugs recovered this week included 3kg of the precursors, an amount sufficient to manufacture 150kg of synthetic drugs, police said.
A 48-year-old man from Glendene will appear in the Waitakere District Court on charges relating to possession of a firearm and ammunition as well as possession of a Class A drug.
Police said further charges were expected once substances were tested.
The compound AMB-Fubinaca was implicated in the mass intoxication of dozens of people in New York in 2016, in which those under the influence of the substance were described as being in a ''zombie-like'' state.
In a New England Medical Journal article into the New York mass intoxication, the authors described the compound as ''ultrapotent''.
Typically, synthetics are dissolved in a solvent and applied to a herbal or plant-based material to make the substance smokable.
Since the compounds were developed, first by pharmaceutical companies who discontinued research then clandestine labs, synthetic cannabinoids have been associated with adverse health effects, the article said.
''More severe clinical features, including psychosis, delirium ... seizures, acute kidney injury, hyperthermia, and death, have also been noted.''
AB-Pinaca is a structurally similar compound to AMB-Fubinaca.