The Australian Federal Police and Australian Border Force have jointly seized 1.2 tonnes of the drug MDMA valued at $145 million in what's potentially the largest drugs bust of the year.
The huge haul of the class A drug, a key ingredient of ecstasy, was found in the Sydney suburb of Hornsby on Thursday.
The seizure followed a rapid investigation that began on Wednesday and involved both Australian and international agencies.
Two Polish nationals, Dariusz Zbroszczyk, 28 and Piotr Latusek, 29, were arrested on Friday and have been charged with offences relating to the importation of drugs.
They faced Parramatta Local Court on Saturday. No application for bail was made and the matter was deferred to the Commonwealth DPP list at Central Local Court on October 19.
It is understood the narcotics originated in the Czech Republic and that a large international syndicate is behind the consignment.
Police said a "very sophisticated concealment method" had been used to import the drugs. They were detected in duffel bags encased in lead and hidden in rolls of aluminium sheeting at a storage facility in the city's north-west.
By Saturday afternoon, 88 sheets of aluminium were awaiting forensic investigation. Of the 22 rolls examined so far, about 250kg of the MDMA - also known as molly - had been found.
Police displayed some 15 bags of evidence containing black refuse bags and large clumps of the drug in its pure crystalline form at Sydney's AFP headquarters on Saturday. They represent just over a fifth of the haul.
The joint agencies would not elaborate on how the drugs entered the country undetected on August 15 and signalled more arrests were possible as they work with international partners in the ongoing investigation.
AFP Deputy Commissioner Justine Saunders said the "significant find" is the equivalent of over 4.1 million tablets of ecstasy and represented the country's fourth-largest haul in history.
"The size of this seizure and the amount of potential harm cannot understated," she said. "It shows the lengths to which criminal syndicates will go to profit off the misery of others - while there is demand for illicit substances, criminals will attempt to supply it."
Deputy Commissioner Saunders said the haul was indicative of the scale of the drug culture in Australia today, with the eastern seaboard of the country the intended market.
AFP Regional Commander Tim Fitzgerald said the size of the find was concerning.
"What we're seeing is a trend of an increase in importation of illicit drugs into Australia," he said.
In 2014, police seized 2.8 tonnes of MDMA as part of Operation KOI, leading to charges against six individuals. Six years earlier, Operation Inca uncovered 4.4 tonnes of MDMA in the largest drugs bust to date.