The Northland ringleader of the operation that produced the largest amount of methamphetamine ever cooked in New Zealand has pleaded guilty to a raft of charges.

Brownie Harding, 38, entered guilty pleas in the High Court at Auckland to six charges of possession of meth for supply, two of conspiracy to supply meth, one of possession for supply, one of supplying pseudoephedrine, and one of participating in an organised criminal group.

At least 9kg of meth with a street value of between $3.2 million and $4.5 million was cooked over 10 weeks in a property in Taipuha Rd at Waiotira, between Whangarei and Paparoa, between September and December 2014.

Two cooks - Jayden Hura and Anthony Mangu - have already been sentenced to 16 years and eight months and 15 years in jail respectively for their part in the drug operation which police named Operation Easter.

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Others sentenced for their roles in the operation included Sharn Stanley Keogh, 27, who acted as a "taxi service" by dropping off people and supplies used in the manufacture of meth. He was jailed for more than eight years.

Harding was remanded in custody and will be sentenced next month.