Seven people, including four from Hong Kong, were arrested after a year-long investigation following a tip-off from US authorities, police said.
The 306 kg of methamphetamine, also known as ice, was Australia's biggest seizure of the drug, while the 252 kg of heroin was the nation's third largest-haul of heroin.
"At the end of the day, there's a lot of 'Mr Mediums' and 'Mr Littles' that work with 'Mr Big'," Deputy Commissioner Andrew Colvin told reporters. "I think we've got a good combination of the people responsible for this importation."
The drugs were found hidden in a shipment of 3,200 terracotta pots at Sydney's Port Botany.
Those arrested were charged with conspiracy to import illicit drugs and holding a commercial quantity of illicit drugs. The charges carry a maximum penalty of life in jail.
"We're talking about a significant quantity of two separate types of substances which generally have different source countries," Colvin said, adding the investigation was continuing and further arrests were possible.
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