Authorities found 123 Central and South American migrants trapped in a trailer in the central Mexican state of San Luis Potosi, Mexico’s immigration agency said Thursday.

Officials from the state attorney general’s office found the migrants in Matehuala, a city on the border of Nuevo Leon, on Wednesday after a local reported hearing cries for help from a locked trailer box.

The majority of migrants rescued were from the Central American nations of Guatemala, Nicaragua, Honduras and El Salvador, as well as four from Ecuador and one Cuban, according to Mexico’s National Immigration Institute. Among them were 34 children.