Police and immigration authorities stopped the truck en route from Malawi in the early hours of the morning in the province of Tete, bordered by Malawi on one side and Zimbabwe on the other, they said.
Amelia Direito, spokeswoman for Tete migration services, said the officials checked the container after hearing banging coming from inside. They found 14 people alive among the bodies of 64 who had died from suspected asphyxiation.
The survivors were now being held at an immigration facility, she added.
Many poor migrants travel via Mozambique on their way into South Africa, the continent's most industrialised economy, where they usually hope to find better work.
The driver of the truck told a local TV station that he had been approached in Malawi by an individual who offered him money to take the migrants into Mozambique."Two people were detained in connection to the incident, the driver and a middleman, who contracted the driver to ferry these people," police spokesman Orlando Mudumane said.