Mexican federal police and immigration agents have raided a train in southern Mexico carrying hundreds of migrants and removed them.

The National immigration Institute says the raid occurred Wednesday in Oaxaca state. It says about 100 migrants "accepted the aid of the institute," but hasn't said whether they were detained or taken for deportation. The rest were allowed to continue on their way, walking.

The agency says that none of the migrants had proper travel documents and that riding on the roof of the train is dangerous, especially for children.

Migrants, mainly from Central America, have returned to hopping the freight train known as "La Bestia" since agents detained over 300 migrants in a caravan walking down a highway last week.