Buses of children began arriving in the early morning hours Friday at Fort Sill as city officials and immigration advocates braced for the arrival of as many as 1,200 immigrant minors.

One bus arrived shortly before 8 a.m. The white passenger bus with “Coach USA” emblazoned on the side pulled through the fort’s entry gates. The bus then pulled up to a building that post officials had earlier identified as the area where incoming children would stay.

Many of the children on the bus appeared to be teenagers. They shielded their faces from the sun as they pulled into the front gates. One young male removed a pair of bright white headphones as he peered out a window towards the sprawling post.

A Fort Sill police officer said buses began arriving at the post around 3 a.m. Friday. Fort Sill is expected to house 600 to 1,200 immigrant minors as the children go through the various stages of the deportation process. The children were caught at the U.S. border while fleeing Central American countries, and workers will try to reunite the children with their families or find them a sponsor.