Manawatū police have discovered two large sheds with more than 1100 cannabis plants in Feilding.
Police were responding to a firearms incident when they found the plants, ranging from seedlings to 325 mature plants ready for harvest, along with more than $800,000 last Thursday.
They also discovered methamphetamine, along with about 8kg of manicured cannabis head, which was ready for supply to markets in Manawatū and Auckland.
Acting Detective Senior Sergeant Dave Thompson said the operation had been a consistent source of cannabis for the local and Auckland market for years.
"This is one of the most significant indoor cannabis operations discovered in the past 10 years," Thompson said.
A 44-year-old man and a 46-year-old woman, who were both granted name suppression, appeared in Palmerston North District Court last week charged with cultivation of cannabis.
They are due to reappear later this month.