(CNN) -- Seven people were injured when two freight trains collided early Saturday morning at a rail intersection in southeast Missouri, causing a highway overpass to collapse, authorities said.
The accident occurred when a Union Pacific train T-boned a Burlington Northern Santa Fe train outside of Scott City, about 120 miles south of St. Louis, Scott County Sheriff Rick Walters said. One of the trains derailed, sending rail cars smashing into an overpass support pillar, he said.
There were no cars on the overpass when it collapsed, but two cars drove into the collapsed structure in the dark, said Trooper Clark Parrott, spokesman for the Missouri State Highway Patrol.
Five of the injured were in the cars, and two on the train. All but one of the injured were treated and released from the hospital, authorities said.
Investigators from the National Transportation Safety Board arrived at the crash scene by midday and were trying to determine what caused the accident.
In the dark, Christopher Cantrell, 22, didn't see the collapsed bridge until it was too late.
His car went airborne and crashed, he told CNN affiliate KFVS.
Cantrell suffered minor injuries. His 19-year-old wife, Victoria, suffered a broken leg and a broken ankle, he said.
The Union Pacific train was hauling auto parts from Illinois to Texas, said Calli Hite, a Union Pacific spokeswoman, told KFVS.
The Burlington Northern train was hauling scrap metal, according to the railway.
Rail where Connecticut trains collided had recent repairs
CNN's Chelsea J. Carter contributed to the story