FORT HOOD, Texas — Fort Hood commanders were in the process of closing roads on the sprawling Army post in Central Texas when a truck carrying 12 soldiers overturned in a fast-flowing flooded creek during a training exercise, killing five and leaving four missing, officials said Friday.

The portion of road on the northern fringe of the post where the Light Medium Tactical Vehicle overturned Thursday hadn’t been overrun by water during past floods, Fort Hood spokesman Chris Haug said. The vehicle resembles a flatbed truck with a walled bed and is used to carry troops.

He said during a news conference Friday that the soldiers were being trained on how to operate the 2 ½-ton truck when it overturned along Owl Creek, about 70 miles north of Austin.

“It was a situation where the rain had come, the water was rising quickly and we were in the process, at the moment of the event, of closing the roads,” Haug said.

Soldiers on training exercises regularly contend with high-water situations following heavy rains, he said.

“This was a tactical vehicle and at the time they were in a proper place for what they were training,” Haug said. “It’s just an unfortunate accident that occurred quickly.”

The bodies of two soldiers were found late Thursday night. Three soldiers were found dead shortly after the vehicle overturned. Three others were rescued by personnel traveling in a separate vehicle and hospitalized in stable condition.

Aerial and ground crews Friday were searching the 20-mile creek that winds through heavily wooded terrain. Army aircraft, canine search teams, swift-water rescue watercraft and heavy trucks were being used.

The Army has not yet released the names of the dead because it’s still notifying relatives.

Maj. Gen. John Uberti said the three injured soldiers could be released from a post hospital later Friday.

“This tragedy extends well beyond Fort Hood and the outpouring of support from the country is sincerely appreciated,” he said.

Parts of Texas have been inundated with rain in the last week, and more than half of the state is under flood watches or warnings, including the counties near Fort Hood. At least six people died in floods last week in Central and Southeast Texas.

Gov. Greg Abbott issued a statement saying the state “stands ready to provide any assistance to Fort Hood as they deal with this tragedy.”

The base has seen fatal training accidents before. In November 2015, four soldiers were killed when a Black Hawk helicopter crashed during a training exercise.