Myanmar police recently confiscated hundreds of millions of dollars worth of illicit drugs in what has become the largest seizure in Asia in decades.

Also included in the bust were “unprecedented” quantities of methylfentanyl, a strong synthetic opioid, CNN reports. The contraband was the result of a three-month operation on a northeast village in Myanmar. 33 people were also arrested in connection with the operation.

Jeremy Douglas, the regional coordinator for the United Nations Office of Drugs and Crime (UNODC), said the number of drugs was “truly off-the-charts.”

Police confiscated almost 200 million methamphetamine tablets, over 500 kilograms of crystal methamphetamine, and 35.5 metric tons and 163,000 thousand liters of precursor chemicals that are needed to produce the drugs. They also found nearly 3,750 liters (990 gallons) of liquid methylfentanyl, a potent synthetic opioid that’s similar to fentanyl. The bust is thought to be the first time authorities have come across such a huge supply of fentanyl or a correlative substance in Southeast Asia.

Because synthetic opioids are more powerful, it’s easier to overdose on them, especially if a drug user doesn’t know what they’re taking. Three overdoses in Bangkok, Thailand last September were thought to be initial proof that fentanyl had been introduced into the city’s heroin supply.

According to Douglas, the quantity of methylfentanyl precursor could have manufactured enough synthetic opioids for a year. “This may be the moment we have feared—synthetic opioids are in the region in a big way,” he said.

Drug production is largely helmed by big criminal syndicates, many of which have moved manufacturing to the Golden Triangle, the border region where Thailand, Laos, and Myanmar join. For years, the area was home to the world’s biggest production of heroin—and is still known for its lawlessness.

According to UNODC, the methamphetamine market in East and Southeast Asia makes $61.4 billion a year, and the COVID-19 pandemic has barely slowed down production and trade.

“While the world has shifted its attention to the COVID-19 pandemic, all indications are that production and trafficking of synthetic drugs and chemicals continue at record levels in the region,” Douglas said.