Mozambican immigration officers have found 64 dead bodies in a shipping container on the back of a lorry that had crossed into Mozambique from Malawi, officials say.
It is suspected that the dead, thought to be Ethiopian, suffocated.
When they inspected the vehicle, 14 people were found alive.
They were on a well-known trafficking route for people hoping to get further south to South Africa.
The immigration service had stopped the container truck in the town of Moatize, according to Tete provincial director of health, Carla Mosse.
She said investigations were ongoing to discover how the occupants died, but said asphyxiation was the likely cause of death.
AmÃ©lia Direito, spokesperson for the National Migration Service in Tete, said the driver had not wanted to stop the vehicle when asked.
She explained that her colleagues had heard noises from the lorry and suspected that migrants might be inside.
Some of the 14 survivors were hitting the container and screaming.