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(Reuters) - Authorities in California have seized a record 1.9 tons of methamphetamine worth some $1.3 billion along with heroin and cocaine, all bound for Australia.

The seizure followed an operation by U.S. border officials and Australian law enforcement and took place on Jan. 11 at the Los Angeles/Long Beach seaport, authorities said on Thursday. The drugs were “artfully” hidden in a shipment of loud speakers.

Four Australians and two U.S. citizens were arrested on Wednesday by the Australian Federal Police (AFP) on suspicion of involvement in the trafficking, authorities said.

“There’s no question that the criminal organization behind this scheme has been dealt a significant blow,” Joseph Macias, special agent-in-charge for Homeland Security Investigations Los Angeles, said in a statement.

The two containers of drugs, hidden inside metal boxes labeled “Single Loud Speakers,” contained 3,810 pounds (1,730 kg) of methamphetamine, about 56 pounds (25 kg) of cocaine and 11.5 (5.3 kg) pounds of heroin, U.S. Customs and Border Protection officials said.

It was the biggest seizure of methamphetamine in the United States and amounted to about 17 million doses, authorities said, adding that if it had reached Australia it would have been worth approximately $1.3 billion.

“Someone’s in TONNES of trouble!,” AFP officials said in a statement posted on Facebook with video footage of the suspects’ arrest. “Luckily we worked with our US buddies and were able to stop the shipment before it reached our shores.”