Portuguese police have made a record seizure of almost nine tonnes of cocaine after intercepting a “narco-sub” off the Azores carrying what is thought to be the largest shipment of the drug ever found on one of the Europe-bound, semi-submersible vessels.

The Portuguese Judicial police said its officers had confiscated the haul in a recent joint operation with the country’s navy and air force that had been conducted in coordination with the US Drug Enforcement Administration and the UK National Crime Agency.

The intercepted vessel eventually sank, taking 35 bales of cocaine with it to the bottom of the Atlantic Ocean. The four men on board – three Colombians and a Venezuelan – were arrested.

“The vessel, which had come from Latin America and was crewed by four foreign nationals, was carrying 300 bales of cocaine,” the Portuguese police said in a statement. “The interception of the semi-submersible occurred at sea, approximately 230 nautical miles from the Azores, under extremely difficult and dangerous conditions due to the current adverse weather conditions.”