Wednesday night's find on a US-flagged boat in a port on Faial island was the biggest of its kind in the archipelago, according to Portuguese authorities.
Four Serbians and a German aged between 29 and 54 were arrested in connection with the haul.
The French finance ministry said the operation was the result of a joint investigation between French customs and Britain's National Crime Agency (NCA) "targeting a Serbian criminal group suspected of trafficking cocaine between the Caribbean and Europe."
The cooperation between French customs and the NCA already led to the discovery of more than two tonnes of cocaine on a tug off the coast of Scotland in April.
Drug hauls are common aboard boats arriving in Portuguese waters from across the Atlantic.