Police say they've found three tonnes of cocaine aboard a ship just off the Spanish coast.

Spanish coastguard video was released on Wednesday after the ship was intercepted 50 miles off the port of Cadiz.

31 people were detained including Bulgarians who were said to have picked up the cocaine in South America and a group of Colombians who were alleged to have masterminded the huge smuggling operation, from Madrid.

A group of Spaniards also detained in the co-ordinated bust were said to have been planning to distribute the contraband cargo throughout Europe.

All 21 crew members were also arrested.