The arrests included 14 men and nine women aged between 21 and 61.
Firearms were also located in Rotorua and Christchurch.
ESR scientists had been working with police in Christchurch to examine and dismantle a scene where it was believed pill-manufacturing was taking place, police said.
Wellington Drugs and Organised Crime squad Detective Senior Sergeant Tim Leitch said they had been monitoring the syndicate for a number of months to collect evidence of their alleged drug-dealing.
"As a result, we have deployed investigators, response and specialist staff across five policing districts to gather evidence and make these arrests.
"The operation will cause significant disruption in the illicit pill market."
The police Asset Recovery Unit seized assets valued at more than $1,875,000 - including four properties, a boat, five vehicles and money held in bank accounts of $230,000.
The operation would have made a significant impact on the distribution of methamphetamine and ecstasy between Bay of Plenty and Canterbury, police said.
The operation followed the successful interception and seizure of $2 million worth of methamphetamine last week.