$20 million in cocaine was allegedly retrieved from a hidden compartment on the exterior of the Maersk Antares in Tauranga on Tuesday night.

The crew of a container ship at the centre of New Zealand's biggest cocaine bust crossed the Pacific unaware of the multimillion dollar stash attached to their vessel's hull by smugglers.

Four people have been arrested after an estimated 46 kilograms of cocaine, with a street value of around $20 million, was seized in a dawn raid in Tauranga on Wednesday morning.

It is the largest cocaine bust in the country's history and comes after a five month operation by Police and Customs.

MATT SHAND/STUFF Police Assistant Commissioner: Investigations, Richard Chambers.

The drugs had been smuggled onto a sea chest attached to the exterior of the 109,000 tonne, Singaporean flagged, Maersk container ship Antares sailing from South America to the Port of Tauranga.

Customs Group Manager Intelligence, Investigations & Enforcement, Jamie Bamford said at 5.45am on Wednesday morning members of a trans-national drug syndicate took a boat alongside the docked vessel to remove the drugs.

The cache was then moved to a Tauranga location for distribution but every move made by the alleged offenders was watched by police.

Matt Shand Customs Group Manager Intelligence, Investigations & Enforcement, Jamie Bamford.

"We're aware this [container ship routes] is a way for drugs to make it into New Zealand," he said. "The ship had come through Columbia, Peru and Chile which are hotspots for this drug."

Police staked out the ship with the expectation members of the drug syndicate would make their move before the vessel's departure time at 4.15pm the same day.

Their wait was rewarded with the arrest of Two Australian men, a Croatian aged in their mid-forties, and one Serbian national in his mid-thirties. All the men had recently moved to Tauranga.

CARYS MONTEATH/STUFF The cocaine had a street value of $20miilion. (file photo)

Subsequent search warrants uncovered another five kilograms of cocaine linked to the men as well as a kilogram of methamphetamine found at an Onehunga address. A large amount of cash, thought to be from a previous importation of 30kg of cocaine, was also found.

All four men were scheduled to appear in Tauranga District Court on Wednesday on charges relating to importing the cocaine and possessing the drug for supply. The charge carries a maximum sentence of life imprisonment.

Assistant Commissioner Investigations Richard Chambers said the the bust was good news for the community.

"Forty six kilograms of cocaine would have done significant harm to our communities," Chambers said.

"These people wanted to establish a cocaine market in New Zealand and now face a lengthy stay in prison."

Chambers said the arrests have dismantled the drug syndicate for good.

While the drugs may be off the streets the police work is far from complete with the focus moving to other smuggles of Class A drugs and the money laundering that supports the illegal trade.

A sophisticated money laundering operation sending hundreds of thousands of dollars out of New Zealand through international criminal money remitters was also discovered. "Inquiries continue and I am confident that further arrests will be made as evidence is uncovered, assessed and actioned," Bamford said.

The two Australian and the Croatian nationals will face additional charges relating to laundering charges.

Police said they believe the crew of the Maersk vessel likely had no idea the drugs had been attached to their hull. "We are not investigating anyone from the vessel," Chambers said.