Mexican police have found 81 Central American migrants locked inside an abandoned lorry near the US border in the northern state of Nuevo Leon.
The migrants, including nine children, were found underneath a false floor, where they had been trapped for two days with virtually no food or water.
The 65 Salvadorans, 14 Hondurans and two Guatemalans all survived, but many were suffering from severe dehydration.
Thousands of illegal migrants pass through Mexico trying to reach the US.
On Monday, 289 illegal migrants were found in a lorry in southern Mexico.
The group from Latin America, including 226 Guatemalans, was discovered during a routine road check in the state of Chiapas.
'Lucky to be alive'
When troops found the abandoned lorry outside the town of Hualahuises in northern Mexico, they were shocked to find 81 illegal migrants under a fake floor covered with decorative plants.
The group had spent two days in complete darkness inside the hidden compartment with only a handful of energy drinks between them to survive on.
Authorities said they were in severe states of dehydration and were lucky to be alive.
Temperatures in the near-desert region reach nearly 35C during the day.
A local government spokesman said the immigrants claimed to have paid between $3,000 and $6,000 to the smuggling gangs in order to reach the US.
The BBC's Will Grant says it is not clear why the people-trafficking operation was abandoned, but the vehicle was dumped not far from a military checkpoint and it is possible that the drivers got cold feet.
The incident provides further evidence of the lengths people will go to reach the US, and of the inhuman treatment of the immigrants by the trafficking gangs, our correspondent says.