Two people have been arrested for alleged money laundering following the seizure of cocaine worth $20 million in Tauranga last week.

Four men were initially arrested when the 46kg load of the drug - the largest single seizure of the drug in New Zealand - was found by police last Wednesday.

The seizure was the result of a five-month-long inquiry by Customs and police.

The two organisations joined forces to carry out investigative work and established that a cocaine shipment would be offloaded from a commercial ship near Tauranga.

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"Customs commenced the operation after an investigation into smaller methamphetamine seizures, resulting in several arrests, identified persons of interest believed to be involved in smuggling and distributing Class-A drugs and money laundering," police said.

Police made the second lot of arrests in Auckland this morning, charging a 29-year-old man from Birkenhead with four counts of money laundering and a 35-year-old female with one charge of the offence.

They are both due to appear in Auckland District Court next week.

Police made the arrest while carrying out a search warrant in the North Shore suburb of Birkenhead this morning.

They also seized a 2017 Honda Civic, a motorbike, a stash of electronics including phones and laptops and several thousand dollars in cash, along with a money-counting machine.

Detective Superintendent Greg Williams, National Manager for Organised Crime Group said the arrests followed an investigation that uncovered a "sophisticated money-laundering operation".

"Police will continue to hold those to account who are responsible for the laundering of funds generated by the drug-dealing activities of criminals."

Williams said the offenders faced a maximum sentence of seven years' jail time.

The four men arrested last week were two Australians, a Croatian and a Serbian national.

Police carried out search warrants in Tauranga, Mt Maunganui and residential addresses in Auckland leading up to the arrests.

A further 5kg of cocaine and a kilo of methamphetamine was found at an Auckland address, along with a large amount of cash.