A large network dealing in cocaine and methamphetamine in Auckland has been shut down after an investigation running for several months, police say.

Operation Ceviche, conducted in three phases, has led to the arrest of 13 people on methamphetamine and/or cocaine charges.

They include a senior patched member of the Hells Angels' Auckland chapter, who has been charged with supplying methamphetamine and possessing the drug for supply.

Detective Senior Sergeant Lloyd Schmid says the operation concluded on Wednesday with the arrest of seven men, and a single seizure of 750 grams of cocaine and $81,000 in cash.

He said the cocaine, with a street value of over $300,000, was a significant find.

"Cocaine is usually picked up in much smaller amounts, so today's find is indicative of people who have been heavily involved in persistent, premeditated career drug dealing," he said.

During the second phase of the operation, police seized 84 grams of cocaine that had been prepared for supply.

"These offenders were creating some fairly identifiable cocaine," Det Sen Sgt Schmid said.

"The drug was being mixed with another substance and moulded into ounce-sized bricks with a hand-made wooden press."

The maximum penalty for the supply of methamphetamine and cocaine is life imprisonment.