Midland, Texas — Federal officials are heading to West Texas to join investigators looking into why a freight train slammed into a parade float carrying wounded veterans, killing four people and injuring 17 others.

Witnesses described a harrowing scene Thursday afternoon as the Union Pacific locomotive bore down on the decorated flatbed truck as it tried to clear the rail crossing on its way to an honorary banquet.

The train was sounding its horn and people on the flatbed truck — mostly wounded veterans and their spouses — were scrambling to jump off before the collision around 4:40 p.m. in Midland, according to witnesses and Union Pacific spokesman Tom Lange.

A preliminary investigation indicates the crossing gate and lights were working, Lange said, though he didn't know if the train crew saw the float approaching.

Two people died at the scene, while two others died at Midland Memorial Hospital, City of Midland spokesman Ryan Stout said. Six people remained hospitalized Thursday night, including at least one in critical condition; the other 11 people injured have been treated and released, hospital officials said.