British police have helped in seizing a record nine-tonne haul of cocaine from a 'narco sub' in the Atlantic Ocean.

The mammoth seizure weighed nearly as much as a school bus and was just 230 nautical miles from the its destination on the Azores archipelago when it was intercepted.

The semi-submersible eventually sank before authorities could take all of its cargo - sending 35 of the 300 packages to the bottom of the Atlantic.

Portuguese police led the operation, assisted by authorities in the UK and US.

The nearly 9-tonne cargo of drugs is "the biggest seizure of cocaine ever in Portugal," a police spokeswoman told the Agence France-Presse news agency.

The boat came from Latin America and had three Colombians and a Venezuelan on board, police said.

They added: "Inside the vessel - 300 bales of cocaine were being transported."

Such vessels have been dubbed 'narco subs' in recent years, with drug cartels using them to take drugs across seas and oceans undetected.

Last year Sky News' Alistair Bunkall reported on the tactics being used smugglers off the Iberian peninsula and how, in November, Portuguese security intercepted the kind of narco submarine that is rarely discovered.

Narco subs had previously been used to ferry drugs north from Colombia to central America and Mexico.

But drug traffickers have been setting their sights further - using them to sail across the Atlantic and Pacific oceans.

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Last March, police said officers had confiscated nearly 6.5 tonnes of cocaine from a semi-submersible vessel off the Azores while bound for the Iberian peninsula.

The British National Crime Agency played a role in that bust - alongside the U.S. Drug Enforcement Administration and the Spanish Guardia Civil.

In 2023, a sub with two dead bodies and nearly 3 tonnes of cocaine aboard was seized off the coast of Colombia.