The joint operation undertaken by police, the Ministry of Business, Employment and Innovation (MBIE) and Immigration led to 10 arrests and the dismantling of drug cultivation and money laundering operations.
Twelve people are facing deportation from New Zealand and as part of Operation Beryl 53 search warrants were conducted at addresses across Waitematā and Counties Manukau districts, police said in a statement.
"As a result of the warrants, 42 significant cannabis crop grows were located with 6886 plants and approximately 10 kilograms of packaged cannabis seized."
Police claim this has a street value of between $16 million and $25 million.
Police said up to $100,000 in cash was also seized.
The 12 deportations involve nine migrants unlawfully in New Zealand, while a further three will be deported this weekend, police said.
Further deportations were being investigated.
Waitematā Acting Detective Sergeant David Coombridge said criminal syndicates involving Vietnamese nationals were primarily using residential properties to set up sophisticated indoor cannabis growing systems.
Some of them had specifically come to New Zealand to participate in organised crime groups, he said.
MBIE national manager compliance David Campbell said the investigation was an excellent example of cooperation across government agencies and the project had led to the investigation of a number of accredited employers.
"Migrant workers need to be aware of those who would seek to exploit them. If you are being asked to pay large amounts of money to an offshore agent to travel and work in New Zealand, it is highly likely that this is part of a fraudulent scam," he said.
Police said they cannot rule out further arrests as part of Operation Beryl.
The 10 people arrested are due to appear in the Waitākere, North Shore and Counties Manukau courts over coming days.