More than a tonne of cocaine has been found hidden inside frozen sharks on a container ship in Mexico.

Navy officers spotted slabs of the drug inside the sharks while carrying out checks with an X-ray machine on cargoes at a container port on the Yucatan peninsula. They donned facemasks and cut open more than 20 carcasses to reveal the drugs haul.

“Those in charge of the shipment said it was a conserving agent but after checks we confirmed it was cocaine,” said Commander Eduardo Villa.

The find underlines how gangs are devising ever more imaginative ways to get drugs into the United States. Sealed beer and fruit cans, religious statues and furniture have all been used.

President Felipe Calderon has ordered 45,000 troops and police to concentrate on crushing the smuggling cartels, which are powerful and well-armed.

Last year 6,300 people died in Mexico in drug-related violence, as smugglers from the northwestern state of Sinaloa led by Joaquin "El Chapo (Shorty)" Guzman fought a turf war with rivals for the lucrative trade.

Yesterday police found the bodies of seven young men who had been shot or beaten to death lying in the street in Gomez Palacio, in the northern state of Durango.

Guzman is trying to gain control of all Mexican and Central American smuggling routes.

Cartel-related violence has spilled over inside the US, affecting states as far north as Arizona, to Washington's concern.

Yesterday the Mexican navy allowed reporters a rare glimpse inside a methamphetamine laboratory they had recently raided. The remote mountaintop site in Sinaloa province had an enormous holding tank containing 13,000 gallons of ephedrine - enough to make more than 300 million individual doses of the drug, or 40 tonnes, with a street value of $1.4 billion.

This is five times greater than the haul last month, when Mexican forces seized 8 tonnes of methamphetamine at a drug lab in Michoacan state.

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