Mexican authorities have found 123 people from neighbouring countries trapped in a trailer in the central state of San Luis Potosi.
They include 34 children, Mexico’s immigration agency said.
Most of those found in Matehuala, 600km (372 miles) north of Mexico City, were from Guatemala, Nicaragua and Honduras.
Officials did not provide details about where the migrants were heading, but many travel through the Americas hoping to reach the United States.
They were found after a local resident reported hearing cries from a locked trailer box, Mexico’s National Migration Institute (INM) said, adding that they were being given food and medical assistance.
It also said they were being provided with accommodation until their situation is resolved.
Some of those found were also from El Salvador, Ecuador and Cuba.
It is unclear if those found in the trailer are part of a 7,000-strong migrant caravan currently making its way from southern Mexico to the United States, most of which are from Central and South America.
Many of those travelling the route are reliant on organised crime gangs, and are vulnerable to kidnapping and extortion.
Ahead of next year’s election, US President Joe Biden has come under attack, particularly from Republicans, for his handling of migration, with the situation at the US-Mexico border being most prominent.
US authorities have detained more than 2.2 million migrants along the US-Mexico border since last October.
The growing number of migrants in cities such as New York has become a challenge for the president who has faced intense criticism over his handling of the border.