Rachel Cachia and Donovan Rodrigues, both 37, and IT worker Stephen Mizzi, 38, briefly faced Melbourne Magistrates Court on Thursday, charged with allegedly importing 1.6 tonnes of methamphetamine and 35 kilograms of heroin hidden in stereo speakers.

Cachia and Rodrigues also face multiple charges of dealing with proceeds of crime and moving goods subject to customs control without authorisation.

The trio were arrested on Wednesday following raids on properties in Darley, Brooklyn, Elwood, Murrumbeena and Sunshine West.

WHERE THE RAIDS TOOK PLACE

The methamphetamine haul - equal to almost 16 million drug deals - is the largest onshore seizure of the drug and was uncovered in Melbourne in April, according to the Australian Federal Police.

"It's almost a quarter of the annual usage in Australia, so this will have an impact," AFP Deputy Commissioner Neil Gaughan told reporters on Thursday.

He alleges Cachia and Rodrigues knew how to exploit the system through their work as independent custom brokers.

"They are trusted insiders in the industry. They (allegedly) used their position of trust to circumvent the border controls that exist within Australia," Mr Gaughan told reporters.

"This vulnerability has been fully removed."

Mr Gaughan described the pair as being "middle to high up" in the drug operation and were likely being "used" by an organised crime syndicate.

READ MORE: RECORD ICE HAUL FOUND IN STEREO SPEAKERS

"There's people above them. We think we know who they are. We'll keep working on the investigation to try to bring them to justice as well," he said.

They were not, however, employed by the state or federal government and did not have security clearance.

The haul was found by Australian Border Force officers inside a sea cargo consignment concealed in stereo speakers.

More than 35kg of heroin, with a street value of $18.5 million, was also unearthed.

It's the largest seizure of heroin in two years.

ABF Assistant Commissioner Sharon Huey said officers were alert to "all types of creative and sophisticated methodologies" used by organised crime syndicates.

"We've seen drugs in highlighter pens, hot sauce and even cowhides. Nothing surprises us," she said.

The consignment came from Thailand, but authorities believe it originated from another southeast Asian country.

An investigation by Thai authorities continues.In court, commonwealth prosecutor Jamey Ellis said police needed extra time to compile their brief of evidence due to the number of phone recordings that needed to be listened to.

"There is a significant amount of listening device and telephone material," he said.

A number of computers were also seized during Wednesday's raids, he said.

The court heard it was the trio's first time in custody.

They did not apply for bail and were remanded in custody to face court on May 7.

-AAP

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