The accidental drug haul off Myanmar's coastal Ayeyarwady region occurred when fishermen spotted a total of 23 sacks floating in the Andaman Sea on Wednesday.
Each one contained plastic-wrapped bags labelled as Chinese green tea - packaging commonly used by Southeast Asian crime gangs to smuggle crystal meth to far-flung destinations including Japan, South Korea and Australia.
Locals were mystified by the crystallised substance in the sacks, said Zaw Win, a local official of the National League for Democracy party who assisted the fishermen and police.
ASF seizes more than 3kgs of crystal meth at BKIA
At first, they assumed it was a natural deodorant chemical known as potassium alum, which is widely used in Myanmar.
"So they burned it, and some of them almost fainted," he told AFP.
They informed the police, who on Thursday combed a beach and found an additional two sacks of the same substance - bringing the total to 691 kilogrammes (1,500 pounds) which would be worth about $20.2 million, Zaw Win said.
"In my entire life and my parents' lifetime, we have never seen drugs floating in the ocean before," he said.
The massive haul was sent on Sunday to Pyapon district police, who declined to comment on it.
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Myanmar's multi-billion-dollar drug industry is centred in eastern Shan state, whose poppy-covered hills are the ideal cover for illicit production labs.
Made-in-Myanmar crystal meth - better known as ice - is smuggled out of the country to more lucrative markets using routes carved out by narco gangs through Laos, Thailand and Cambodia.
A study by the United Nations Office on Drugs and Crime says that Southeast Asia's crime groups are netting more than $60 billion a year - a conservative estimate, according to experts - thanks to a sophisticated smuggling and money-laundering operation.
In March, Myanmar authorities seized more than 1,700 kilogrammes of crystal meth worth nearly $29 million, which police said at the time was their biggest drug haul this year.
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