Survivors of a roughly 75-car pileup that left at least 15 people dead saw the road vanish behind a shroud of fog, then heard nothing but "bangs and booms" as one vehicle after another collided.

At least 50 people were injured in Tuesday's chain-reaction crash, Tennessee's worst traffic accident in at least 20 years. At least six tractor-trailers burst into flames, and the fire raced across more than two miles of Interstate 75, reducing dozens of vehicles to burned-out shells.Authorities pulled bodies from the wreckage for hours Tuesday and resumed looking for victims Wednesday. They said it was likely more would be found in the twisted, charred hunks of metal and the death toll could rise.

"It's just so much destruction in one place, all up and down the highway," said firefighter Brent Runyon. "It's just three miles of hell."

Citizens in surrounding communities lined up to donate blood and offered clothing and lodging for survivors, and a team from the National Transportation Safety Board arrived to investigate the disaster.

Survivors said the crashes began when motorists hit astretch of highway shrouded in fog.

"All of a sudden, everybody started stopping right in front of us," said Ralph Fisher of Cleveland, Tenn., who managed to get to the side of the highway as vehicles all around him collided and burst into flames. "After that I started hearing bangs and booms from everywhere."

The stretch of highway 40 miles from Chattanooga has long been notorious for dangerous fog and has had several chain-reaction crashes over the years. Runyon recalled that several people were killed in a similar pileup there in 1979.

The section is lined with flashing yellow warning lights.

Authorities said the crashes began on the southbound side of the highway when a tractor-trailer rig jackknifed. The wrecks then spread to the northbound lanes.

Most of the cars and trucks did not burn, but many were crushed beyond recognition. Others were strewn along the shoulder and center divider at bizarre angles, some of them wrapped around each other likes layers of an onion.

Many people leaped from their cars after stopping and scrambled to safety in the median. At least one person was struck by a car as he stood outside his vehicle.

"There was a lot of confusion," said Clyde Wilder, a truck driver from Knoxville. "There were people scattered out in the fields on both sides. People were checking cars. They found one boy over here with broke legs and broke ribs."

"When we got here, it was so foggy you couldn't see your hand in front of your face," said Hal Munck, director of the Bradley County Office of Emergency Preparedness.

Trucker Riley McSpadden of Chicamauga, Ga., and his partner were heading to Dalton, Ga., with a load of carpet yarn. McSpadden, 31, sleeping in the cab while his partner drove, said he was awakened by cries for help.

"I jumped out and went to the truck in front of us and saw that the guy was pinned in by the steering wheel," he said. "The inside of the cab was already on fire. I just told him, `Bud, there's no way I can help you.' And I just shut the door."

Within seconds, McSpadden said, fire engulfed the man and his truck.