A raid by Mexican authorities on a Maersk boxship discovered 102.5kg of cocaine on board - but also a more unusual cargo.
Two dockworkers were also found inside the box on the 9,640-teu Svendborg Maersk (built 1998) in Manzanillo on 2 July.
The men were apparently watching over the illegal cargo, but it is not clear when they boarded.
Mexican newspaper El Universal said the drugs are worth $1.2m.
Maersk has confirmed two men were found hidden in a container.
But it is not disclosing further details while the investigation continues.
Tip-off about haul
"We are cooperating with the Mexican authorities responsible for the case," a spokesman said.
Mexican media said officials were acting on a tip off about drugs being on board.
The vessel had arrived from Balboa in Panama and had previously visited Buenaventura in Colombia.
The two dockers have been detained.
Seizures of drugs are an occupational hazard for big box lines.
TradeWinds has reported on four previous incidents involving the company's vessels in the last four years.
