"It was a semi-submersible vessel that floated just underneath the surface of the water," said Kevin Ness, a spokesman for the U.S. Coast Guard in Alameda, California.

The craft was about 15 metres long and "painted blue to hide it under water," he told Reuters.

Ness said the drug traffickers sank the vessel before U.S. Coast Guard officials could get there.

Video: Cocaine-Filled Sub Stopped in Pacific

Officials detained four men found floating in the water along with 11 bales of cocaine weighing around 550 kg.

"The rest is now at the bottom of the sea," said Ness.

The U.S. Coast Guard, which spotted the vessel on Monday in the Pacific Ocean about 480 km southwest of the Guatemala-Mexico border, estimated the value of the recovered cocaine at more than $350 million.

About 75 per cent of cocaine processed in Colombia passes through Central America on its way to the United States and smugglers keep coming up with sophisticated tricks to try to avoid getting caught.

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