More than $12 million worth of the drug GBL - commonly known as "coma in a bottle" - was disguised as liquid fertiliser in a shipment sent from China before it was discovered in Sydney, authorities say.
NSW Police on Thursday said it was the largest seizure of gamma-butyrolactone in the state and possibly the biggest ever Australian haul.
Acting Assistant Commissioner Stuart Smith said the seizure had prevented "at least a million deals" being sold at dance festivals and nightclubs.
"This is so pure," Mr Smith told reporters.
He said the drug, which metabolises in the body as GHB, could be deadly. It's capable of melting plastic.
"GBL is a dangerous drug type ... it can cause coma, or can cause death if mixed with alcohol," he said.
"It is a significant seizure of a highly dangerous drug. They call it paint stripper."
NSW Police and the Australian Border Force made the discovery after analysing importations from China to a number of companies in Sydney's southwest.
ABF officers allegedly found the 4000 litres of GBL - also referred to as liquid ecstasy and fantasy - in a consignment declared as liquid fertiliser a week before Christmas.
Border force regional NSW commander Danielle Yannopoulos said authorities were intercepting GBL at the border on a "very regular basis".
"This is clearly not a boutique job," Ms Yannopoulos said.
Mr Smith said GBL was one of between three and five drugs found in preliminary toxicology reports of the two young people who died in September 2018 at Sydney dance festival Defqon.1.
The record seizure comes several months after police raided two clandestine labs producing MDMA in Sydney arresting two middle-aged men.
Mr Smith said those raids helped guide police and the ABF to investigate large-scale business imports to Sydney's southwest.
The two men have been refused bail and are expected to face court in February.