Police found three shipping containers containing 370 mature cannabis plants and 70 seedlings and clones at a house near Whangarei last week.
An anonymous tip off to Crimestoppers led police to search the Whareora property, where they found two underground shipping containers, buried under a polyhouse, and an eight metre shipping container above ground, near a boundary fence.
They arrested a 45-year-old man, charging him with cultivation of cannabis.
They also searched another property owned by the man and found four unsecured firearms and some ammunition.
Police encourage people to call Crimestoppers if they have information on criminal activity and want to remain anonymous.
"We were able to use the information provided and then carry out further inquiries which led to the discovery of the plants and the arrest of an offender," Whangarei Organised Crime Unit head Detective Sergeant Mike Blowers said.