Portuguese police have apprehended a "narcosub" carrying around 1.7 tons of cocaine off the coast of Portugal, officials said on Tuesday.

The mission by the Judiciary Police also led to the arrest of four individuals in the middle of the Atlantic Ocean.

The Portuguese Navy and the Air Force collaborated in the operation that took place on October 30.

Operation “El Dorado” as authorities called it, also involved the US Drug Enforcement Administration and Joint Interagency Task Force South, as well as the UK’s National Crime Agency.

Authorities believe the drugs were heading to the Iberia Peninsula, which would then work as an entry point for other European countries.

The so called “narcosub” was described as a makeshift fragile boat and its condition didn’t allow for it to be towed back to shore.

In March of this year, authorities also apprehend another semi-submersible type of boat carrying over six tons of cocaine off the coast of the Azores archipelago.