More than seven tonnes of cocaine have been seized by the US Coast Guard Authorities off the east coast of El Salvador, which were loaded on a submarine-like vessel.

The vessel was tracked in international waters by US Coast Guard, Customs and Border Protection and US Navy personnel as it made its way through the area.

Reports show that smugglers have made increasing use of home-made submarines or semi-submersibles to evade radar and sonar detection.

The semi-submersible vessels are barely breaking the water's surface as they slip through the Pacific or the Caribbean on their way to the US.

After the latest seizure, which was made last Saturday (July 18), the US authorities found 274 bales packed with 7,650kg (16,870 pounds) of cocaine worth hundreds of millions of dollars. Four suspected smugglers were taken into custody.

This type of semi-subs used for drug-smuggling were first spotted in the 1990s and were designed to sit underwater with only a cockpit and exhaust pipes above the water.

US Authoritites Seizes 'Narco Sub' with 8 Tons of Cocaine

During the last 2 decades Colombian police have found true submarines under construction capable of diving 300 ft.