MEDFORD, Okla. -- A propane truck heading across tracks near Highway 81 in Grant County was slammed by a Union Pacific train Friday, killing two people and injuring another, the Oklahoma Highway Patrol said.

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"It blew the semi tanker apart," Oklahoma Highway Patrol Lt. George Brown said. "The cab was on one side of the train and the tanker on the other."

Mike Honigsberg, emergency management director for neighboring Garfield County, said the two people aboard the train were killed.

The injured truck driver was flown by medical helicopter to Via Christi Regional Medical Center-St. Francis in Wichita, Kan., with third-degree burns over at least 50 percent of his body.

The propane tanker had just filled at a gas station, witnesses said, heading southbound down U.S. Highway 81 before colliding with the train near a gas factory three miles south of Medford.

Donna Kush, another Union Pacific spokeswoman, said the two-person crew sounded the horn and began trying to stop the train 140 feet before impact while going about 37 mph.

Honigsberg said the emergency actions they took as the locomotive approached the tanker prevented the train from becoming a runaway after they died.

"In my opinion, that was a heroic effort because if they didn't, there was nothing to stop that train between here and Enid," which is about 35 miles south of Medford. "They probably prevented another major catastrophe."

Honigsberg said officials believe the truck driver had just filled up the tanker at the ConocoPhillips LP gas facility next to the accident site. The liquid propane facility was shut down briefly.

"The explosion was massive. It blew part of the tanker a quarter-to a half-mile away," Honigsberg said.

All that was left of the locomotive was a burned-out shell. The explosion blackened the first three cars and left a large crater in the ground.

Joan Kretchmar said she was watering her flowers in front of her house less than a half-mile from the accident site when she heard a tremendous explosion, turned around and saw a giant ball of fire headed toward her.

"When I saw that ball of fire, it was devastating. It looked like it was coming right at me," Kretchmar said.

She said she turned and ran to her family's lawn mower shop on an adjacent piece of property.

"I was hysterical. I didn't know what to think," she said.

Korina Schneider of Medford was driving south on U.S. 81 when she saw a ball of fire leap into the sky.

"All of the sudden there was an explosion all across the highway," she said. "It looked like something you'd see in a movie. I was clutching my steering wheel and saying 'Oh my God.'"

The 76-car Union Pacific train was traveling from Wichita, Kan., to Fort Worth, Texas, with a load of flour, wheat, possible metals and some flammable substances, Espinoza-Williams said. None of the flammable substances leaked from the train cars. Brown said some of the cars were hauling ethanol and methanol.

Union Pacific owns the train and said there was a camera on board. Company investigators said conductors did follow proper procedures and that the train had been checked before leaving Wichita on Thursday night.