MEXICO CITY (AP) — Mexico’s immigration agency said late Friday it found 491 migrants being held at a compound by the side of a highway east of Mexico City.

All but six of the migrants were from Guatemala; the others are Hondurans.

There were 277 children and adolescents among the migrants, most of whom were traveling with relatives. But there were also 52 unaccompanied minors.

The migrants were being held in a walled compound near the city of Puebla, along a route frequently used by migrant smugglers. The migrants were taken to offices of the National Immigration Institute.

Smugglers in Mexico frequently hide migrants at such compounds until they can be taken aboard buses or trucks to the U.S. border.