Gang members, a grandmother and beneficiaries were all arrested in the country's largest cannabis bust which resulted in the seizure of drugs with a potential worth of $130 million.

More than 2500 people were arrested in the six-month crackdown, which has made a massive dent in New Zealand's cannabis supply, police said.

As well as arresting 2573 people, police also confiscated 280 kilograms of plant material, estimated at $5.6m, and destroyed more than 130,385 plants and seedlings with a potential street value (at maturity) of up to $130m.

Following 2009's Operation Lime, which targeted businesses and individuals selling cannabis-growing equipment, the latest raids were dubbed Operation National, which was the largest operation of its kind, Detective Inspector Paul Berry said.

Police targeted drug dealers working out of houses. The crackdown was complemented by Operation Kelly, which used aircraft to spot cannabis crops during the growing season.

When they raided homes police found multi-million dollar operations, including one which was allegedly run by a Wellington grandmother and her family and another by a Southland resident, who had accumulated millions of dollars in assets despite being unemployed for more than 20 years.

Every gang in the country was involved, including the Mongrel Mob, Head Hunters and Rebels, Berry said.

"This is bread and butter for the gangs. This is how they make their money."

Police also found 248 children, who would have watched their parents grow drugs and sell them at the door, Berry said.

Many of those children had been referred to CYFs.

Police also discovered more than 300 firearms and other illicit drugs, including 1.4kg of methamphetamine, 321 LSD tabs and 4150 ecstasy pills.

They seized 14 properties, worth a total of $4.6m, eight cars, a boat, and cash and bonds worth more than $1m, some of which was seized under the Criminal Proceeds Recovery Act.

"When you put the two lots of results together - both Operation National and  Operation Kelly - that is a significant disruption to the supply chain," Berry said.

"Police recognise that cannabis continues to be a major issue for New Zealanders and causes widespread harm to the community through health issues caused by addiction and related crime such as thefts and burglary."

A recent UN report said New Zealand had one of the highest number of cannabis users in the world, and police were committed to bringing that number down. Many of those arrested had already appeared in court. Operation National was just the start of a major crackdown, Berry said.

"It's a social evil, not a social good," he said.

"We remain committed to disrupting the business end of illicit drugs - that means targeting the growers and the dealers."

By targeting dealers, police believed they were directly hurting the potential for organised criminal groups to operate successfully, Berry said.

All 12 police districts were involved in the operation, and some have already released their results.

- © Fairfax NZ News