Image copyright Agencia Mexicana Image caption Authorities said the migrants were found on the second part of the trailer
Mexican authorities have found more than 600 migrants who had apparently been hidden in two trailers in the Gulf Coast state of Veracruz.
Officials said the migrants were from Honduras, Guatemala and El Salvador.
Veracruz police spokesman Marco Antonio Fortuna said the discovery took place on Friday.
Veracruz police said the migrants had paid a man an extra amount for the opportunity to get into Mexico illegally.
Many migrants enter Mexico illegally through the state of Tamaulipas, before continuing north toward the US.
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The reported discovery was made in the town of Tijimal, which lies close to the Mexico-Guatemala border.
Police said it appeared that the migrants were taken into the US by a human smuggler.
The migrants included 104 children, including three newborn babies, according to media reports.
Activists in the town, who have been providing assistance to the migrants, said the group was covered with the belongings of those who had been deported from the US, and had been left behind by smugglers.
Migrants who enter Mexico through Tamaulipas are often forced to leave behind their families and other belongings in Mexico.
In recent months, Mexico has seen a number of high-profile cases in which migrants were deported without the proper paperwork.
The Honduran deputy attorney general was reportedly arrested last month for helping illegal migrants return from Mexico.
Several people have also been detained after a trip across the US-Mexico border turned into a confrontation at the international boundary.
The migrants and border guards were allegedly involved in a violent clash this month that left one immigrant dead.
Some people told the BBC’s Mexican news service about how they had illegally entered the US without any documentation.