"This will take some time and we are not in a position to comment any further on this for operational reasons.
"As these matters are before the courts we are unable to make any further comment."
Sutton said another "significant" arrest had also been made in the war against synthetics.
They say they have seized product that would have had a street value of $1.5 million had it been sold.
The first arrest comes as part of Operation Tiger, which is an ongoing operation to target the importation of psychoactive substances.
The investigation was initiated after Customs seized a kilogram each of AMB-Fubinaca and AB-Pinaca, the psychoactive substances often used to make synthetic drugs.
Following this, police have been working in the background and last month nine search warrants were executed in Auckland, Palmerston North and Christchurch.
"Our most significant find was a storage unit in Rodney where 11kg of finished synthetic drugs were found and another 1kg of AMB-Fubinaca," said Detective Inspector John Sutton of the Waitemata Police.
"The 1kg located by police and the 2kg by Customs would be sufficient to manufacture around 150kg of synthetic drugs, that's approximately 75,000, 2 gram doses of the drug, which is worth a street value of $1.5 million.
"The 11kg of finished synthetic drugs located in the storage unit would have had an approximate street value of $110,000."
A 58-year-old man was arrested yesterday and charged with four counts of importing a psychoactive substance, possession of a psychoactive substance for supply and manufacturing a psychoactive substance.
He will appear in North Shore District Court on Wednesday September 20.
Sutton said Operation Tiger was ongoing and police cannot rule out the possibility of further arrests as inquiries continue.
He wanted to thank Customs for their assistance with Operation Tiger.
"We will continue to work closely with our partners, to reduce the impact and harm this drug is having on families and whanau," he said.
"We also continue to urge our community to tell us who is selling these drugs.
"We need your help to catch these offenders so please do not hesitate to contact us with any information, we can assure you, it will be taken seriously.
"If you have any information that can assist police in catching these offenders, please contact your local police station, or call Crimestoppers anonymously on 0800 555 111.
"If you have any concerns about the health of someone who has consumed synthetic drugs, call 111 and ask for an ambulance."
