More than 23.5 metric tons of cocaine have been seized in the Mexican port city of Manzanillo, in what authorities are calling the biggest single haul of the drug ever.

Cargo containers filled with packets of the drug were discovered during a routine inspection.

Mexican customs officials noticed shipping containers listed an improbable mix of contents for a Hong Kong registered ship that arrived from Colombia. They searched the shipping containers with a special gamma-ray scanner and detected suspicious shapes inside. When they opened the containers, they found 21,116 wrapped packages of cocaine.

Authorities say it's the biggest cocaine bust in history.

It is presumed that the cocaine belonged to Mexico's Pacific drug cartel. Now it is under the supervision of Mexico's navy.

President Felipe Calderon has made the fight on drugs and organised crime a cornerstone of his administration, and the U.S. unveiled a proposal earlier this month to give Mexico $1.4 billion to fight narcotics-related crimes.

The U.S. Congress has yet to approve George W. Bush's request for an initial instalment of $500 million for the plan.

Following the seizure U.S. President George W. Bush called his Mexican counterpart, Felipe Calderon, to congratulate him on the success of the operation.