Protesters briefly block bus leaving migrant detention center in Texas

Protesters stood in front of the bus and yelled, "Set the children free" and "Shame on you" at Border Patrol officers. The Border Patrol ended up surrounding the bus so it could back up and go out the other end of the street.

Authorities didn't say who was on the bus or where it was going, but one protester told CNN she could see small children through the darkened bus windows. She said some of the children waved at her and she told them, "You are not alone" in Spanish.

CNN was reaching out to federal immigration officials for comment.

"It was very difficult to see," said Denise Benavides of Dallas, who said she's a member of the League of United Latin American Citizens.

Benavides said she didn't know where the bus was going but "that's something we'll look into -- what's going on and where are they taking these children."

Uniformed officers arrived to calm the situation and nobody was arrested.

More than 1,100 immigrants -- including children -- were being held at McAllen when reporters were allowed inside on June 17.

The Department of Homeland Security processes and detains immigrants accused of illegally crossing the border at the facility near Brownsville, Texas.