Australian police say they have seized a stash of crystal methamphetamine and heroin with a street value of up to $525 million.

Authorities said Tuesday the drugs were smuggled into the country in a shipment of terracotta pots, but did not say where the shipment originated.

Police arrested seven people, including four from Hong Kong and three Australians, in connection with the case. They face up to life in prison if convicted.

The 306 kilograms of crystal methamphetamine was the largest amount of the drug ever seized in Australia, while the 252 kilograms of heroin was the third-largest haul of that drug.

The seizure came after a nearly year-long investigation that began with a tip from U.S. authorities.