The haul of cocaine, one of the largest ever intercepted in Spain, was inside a metal structure designed to escape detection from scanners.
But customs agents detected a large quantity of stacked goods that practically filled the container, so they forced it open.
The drug smugglers had planned a route designed to make the discovery of the cargo's true contents as difficult as possible. From Suriname it travelled to Panama and from there to Algeciras. Its next destination was Leixoes in Portugal, from where it was to be transported by road back to Spain.
Three people have been arrested, customs agents said.
(Reporting by Emma Pinedo; editing by Charlie Devereux and Ed Osmond)
