MIAMI, Okla. (AP) — At least three people were killed Thursday when the pickup truck they were in drove off of a snow-covered interstate highway bridge and plunged 80 feet into an icy river below.

Ottawa County Sheriff Terry Durborow said the truck jumped a guard rail on Interstate 44 in northeast Oklahoma at about 6:30 a.m. and fell into the Spring River. The truck was partially submerged.

"I don't know if she lost control of her vehicle or not. She just jumped the guard rail off that bridge," Durborow said. The harsh weather conditions, including 20 inches of snow on the ground and temperatures of minus-9 degrees, made rescue attempts difficult.

"It's probably the worst conditions I've seen, and I've lived here all my life," he said.

Durborow says from five to eight people were in the truck. Survivors were taken by ambulance and helicopters to hospitals, said Oklahoma Highway Department spokesman Lt. George Brown.

The interstate was rendered impassable by the powerful blizzard that barreled through Oklahoma and much of the nation Tuesday and Wednesday, and authorities had to help bring hundreds of stranded motorists on I-44 to safety. It's westbound lane, in which the pickup was driving, wasn't reopened until late Wednesday.

Brown wouldn't speculate on whether the highway was re-opened prematurely, given the continuing severe conditions.

Motorists who witnessed the accident said they peered over the side of the bridge and spotted six people outside of the truck in the icy water and another two people inside the vehicle, Brown said.

"This is a fall of 80 feet or better ... that alone is a very dangerous type of crash. This is a very traumatic crash," Brown said.

"The rescue teams got a small boat, hoisted it down in the water and started the recovery," Brown said.

"The ground temperature was 11 degrees below zero, so it would take second to become hypothermic in this water and ice."

Copyright 2011 The Associated Press.