Mexican authorities have recovered two packages believed to contain cocaine from a cargoship in Altamira.
The navy said 49kg of the drug was discovered among iron ore in the hold of the 38,000-dwt UBC Tokyo (built 2005) after a search by dogs, Mexican media reported.
The vessel had arrived from Barranquilla, Colombia.
There is no suggestion the crew was involved in any way.
US operator United Bulk Carriers has been contacted for further information.
Earlier this month, Mexico seized 23 tonnes of the deadly painkiller fentanyl from an unnamed Maersk boxship.
The drug was contained in 931 bags disguised as a cargo of calcium chloride, which is used in road salt.
