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Thirty people have been arrested, thousands of dollars seized and more than 10,000 cannabis plants destroyed in sweeping police stings.
Police in Auckland said their month-long operation netted 10 tonnes of cannabis and shut down 120 grow houses.
They said it was so much cannabis that four trucks a week were needed to take it away in the Waitematā district alone.
Officers say the plants were largely hidden in plain sight in average-looking rental properties in areas like Pōkeno in the south, Pakuranga in the east, Henderson in the west and Torbay to the north.
More than half a tonne of cannabis was located by Auckland City Police at a warehouse in the Penrose area.
Over a month, police have shut down 120 cannabis grow houses in Auckland. Photo: Supplied / NZ Police
Further south, Counties Manukau Police destroyed more than 140 kilograms of cannabis and 4200 plants.
Police said most of the people arrested were from Vietnam and were now going through deportation.
They say cannabis grow houses linked to Vietnamese organised crime are increasingly coming to their attention.
"Police efforts have dealt a significant blow to the pockets of organised crime figures and their associates, denying them a payday of more than $50 million," McNeill said.
He said growing cannabis was not the only illegal activity taking place on the properties.
"We know these rental properties are often fitted out with shoddy electrical wiring, fuelled by stolen power which is diverted from other properties.
"It's not only illegal but poses very real dangers to those operating the grow houses and innocent members of the community."
In many instances police have been called to residential house fires after evidence of a cannabis grow operation was discovered, he said.
Locations of growhouses shut down by police over a month. Photo: Supplied / NZ Police
McNeill said in many cases private landlords weren't carrying out basic checks before or during tenancies.
"If tenants move in and turn your house into a growing operation, you risk being liable in the event of a fire or significant damage."
He said landlords should do reference checks, meet tenants face-to-face and check IDs, carry out credit and income verifications and regularly inspect their properties.
Police say the operation has taken $58 million out of organised crime.
Sarina Gibbon, from law advisor Tenancy Advisory, said the advice from police was common sense but some landlords were desperate to fill their properties.
"Certainly in Auckland, we're seeing the stripping away of rental demand so landlords are incentivised to act more carelessly because they are needing to get tenants in, we're no longer in than environment where you can literally stand up an open home and 20 people come along and fight each other for the tenancy," she said.
"So I can see in this instance that some private landlords without adequate support and experience in the industry feeling the financial pressure of having to rent out their property sooner rather than later may be bypassing some critical aspects of tenancy checks."
Gibbon, who is also from the Auckland Property Investors Association, said other landlords might not understand what their checks on prospective tenants were revealing.
"What I'm seeing is people are simply not asking the right questions at reference checking stage or even not understanding credit reports, so it's almost like you can carry out the checks but unless you do it meaningfully the resulting data isn't going to really inform you a heck of a lot," she said.
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