The Mexican Navy has detected and seized more than one ton of cocaine hidden in bellies of frozen sharks on board a container ship coming from Costa Rica.

X-ray machines and sniffer dogs helped detect the hidden drugs on the Marshall Islands-flagged Dover Strait after it docked at the Gulf coast port of Progreso in Yucatan state, Mexican Navy Commander Eduardo Villa said Wednesday.

"Those in charge of the shipment said it was a conserving agent but after checks we confirmed it was cocaine," Villa said, according to BBC.

Sailors cut open 30 sharks and found nearly 2,000 pounds (893 kilos) of cocaine slabs in their bellies.