The coast guard said they had found “two tonnes” of what they suspect to be pure cocaine on a Norwegian-flagged vessel which had departed from Mexico and made stops in Ecuador, Panama and China.

The operation was launched after South Korean authorities received intelligence from US agencies – the FBI and homeland security investigations (HSI) – that the vessel was carrying hidden narcotics.

The coast guard and customs service coordinated a large-scale search operation “consisting of a joint search team of 90 officers… along with two drug-sniffing dog units”.

After the vessel docked at an east coast port in South Korea, the team immediately boarded the vessel and “discovered a hidden compartment behind the ship’s engine room”.

The drugs were packed in 56 sacks, each holding some 30kg to 40kg of the drug, authorities said, bringing the total haul to around two tonnes.

“Preliminary field tests confirmed the substances as suspected cocaine,” a coast guard official told AFP.

“The seizure is the largest in history, about five times bigger than the previous record which was 404kg of methamphetamine,” a customs service official told AFP.

The estimated street value is 1 trillion won, they added.

Authorities have launched a joint investigation team to question the vessel’s captain and crew about the origin and intended destination of the drugs, and the route used to transport them.

Investigators also said they are looking into potential ties to international drug trafficking syndicates and will expand cooperation with the FBI and HSI.

South Korea has long ranked among the countries with low drug use globally, thanks to its strict laws and strong social stigma.