The Mexican navy has seized more than a tonne of cocaine hidden inside frozen sharks.

Navy officers cut open more than 20 shark carcasses filled with slabs of cocaine after checking a container ship at a port in the southern Mexico state of Yucatan, the navy and Mexican media said.

"We are talking about more than a tonne of cocaine that was inside the ship," Eduardo Villa, a navy commander, said after X-ray machines and sniffer dogs helped uncover the drugs.

Drug gangs are finding new ways of getting drugs into the US, including in sealed beer cans and religious statues, as Mexico's military cracks down on the cartels moving South American narcotics north.

The Mexican navy also said they have uncovered a large methamphetamine labaratory, with enough ephedrine to produce more than 40 tonnes of the drug.

The navy said they found 12,905 gallons (49,640 litres) of ephedrine, a chemical used to make methamphetamine, in an enormous tank on top of a mountain in the northern state of Sinaloa

Felipe Calderon, the Mexican president, has sent 45,000 troops and federal police to try to combat powerful smuggling cartels.

But heavily armed traffickers have continued to battle over the lucrative routes, with the violence spreading into the US.

Some 2,750 people have died in drug violence in Mexico this year.