A homemade narco-submarine, the first of its kind to be found in Spain, has been seized by police in Malaga.

Police came across the 9-meter-long craft last month while it was being built in Malaga, on southern Spain's Costa del Sol, during a broader international drug operation involving five other countries and the European Union crime agency Europol.

The three-meter-wide semisubmersible craft, capable of carrying up to 2 tonnes of drugs is made of fiberglass and plywood panels attached to a structural frame, has three portholes on one side and is painted light blue. It has two 200-horsepower engines operated from the inside.

Rafael Perez, head of the Spanish police, said the vessel had never sailed.

"We think it was going to go into the high seas to meet a mother ship to take on board the drugs," probably cocaine, before returning to Spain, Perez told reporters.

"It is like an iceberg," he said of the vessel's structure. "In practice, nearly all of it goes under water apart from the top, which is the only part of it that would be seen from another ship or a helicopter."

Police confirmed that it is the first semisubmersible craft of its type found in Spain although similar drug-smuggling vessels have in the past been discovered in the Atlantic Ocean, especially off Central and South America. They sit low in the water to escape detection and are rarely able to submerge fully.

The wider police operation against the alleged international smuggling ring netted hundreds of kilos of cocaine, hashish and marijuana in various places in Spain, with 52 people arrested.

Spanish police said in a statement that police in Colombia, the United States, the United Kingdom, the Netherlands and Portugal also were involved in the operation.