Rescuers picked through the rubble in the southern United States on Wednesday, a day after a deadly string of tornadoes destroyed houses, uprooted trees and overturned transport trucks.

The death toll climbed to 55 by Wednesday evening. Thirty-one people died in Tennessee, authorities said, and 13 others perished in Arkansas, seven in Kentucky and four in Alabama.

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James Devaney searches through the debris of his daughter's home in Lawrence County, Ala. on Wednesday. Devaney's daughter, Becky Coleman, was killed, along with her husband and son, when the tornado hit. ((Gary Cosby Jr/Decatur Daily/Associated Press) )

Hundreds more were injured in the storms that struck Tuesday night, as millions of Americans voted in the Super Tuesday primaries.

Twisters also struck in Mississippi, although no deaths were immediately reported.

National Guard and rescue teams went from home to home in the devastated areas, looking for injured survivors and bodies among the heaps of debris.

Ray and Nova Story tried to drive their badly injured uncle to a hospital after a tornado destroyed his mobile home near Lafayette, north of Nashville, Tenn. The 30-minute ride turned into a two-hour ordeal, as neighbours used chainsaws to try to clear a path through the debris so that the Storys' pickup truck could get through.

"He never had a chance," Nova said of her uncle, Bill Clark. "I looked him right in the eye and he died right there in front of me."

The United States has not seen such a deadly barrage of tornadoes since May 31, 1985, when 76 people were killed in Pennsylvania and Ohio.

On Tuesday, there were 67 eyewitness accounts of tornadoes, but some of those were probably twisters that were counted more than once, said Oklahoma meteorologist Greg Carbin. The actual number is probably more like 30 or 40, he said.

President pledges government aid

U.S. President George W. Bush expressed his condolences Wednesday to the families of those who died and pledged that his government would come to their aid. He said he called the governors of Alabama, Arkansas, Kentucky, Mississippi and Tennessee to assure them help was on its way.

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The arches of McDonalds in Gassville, Ark., lie on a car on Tuesday after a storm ripped through the city. ((Kevin Pieper/Baxter Bulletin/Associated Press))

"The American people will hold those who suffered up in prayer," Bush said. "This government will help them."

The Federal Emergency Management Agency said Wednesday it was sending teams into the region to assist local authorities and assess the damage.

The storms were part of a rare spasm of winter weather that stretched over the south and central regions. As the extent of the damage quickly became clear, several U.S. presidential candidates paused in their speeches to supporters to remember the victims.

In Castalian Springs, Tenn., a passerby discovered a crying baby lying alone in a field across from a demolished post office. Emergency officials said the baby seems unharmed, although they have not been able to locate the parents. 

The death toll in Arkansas included a couple and their 11-year-old daughter who died when a tornado hit their house in Atkins, a city of 3,000 in the centre of the state.

"Neighbours and friends who were there said, 'There used to be a home there,'" Pope County coroner Leonard Krout said.

'Glass just exploded'

Twenty students were trapped in a battered dormitory at Union University in Jackson, Tenn., until they were finally freed. 

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Students walk past a collapsed girls dormatory at Union University in Jackson, Tenn. on Wednesday. ((Jim Weber/Commercial Appeal/Associated Press))

Danny Song was pinned for an hour and a half until rescuers dug him from the rubble.

"We looked up and saw the funnel coming in. We started running and then glass just exploded," he said. "I hit the floor and a couch was shoved up against me, which may have saved my life because the roof fell on top of it."

At least two dormitories on campus were destroyed, but the school's president, David S. Dockery, said the students were well-versed in evacuation drills, as the campus had been hit by tornadoes before.

Fifty students were sent to hospital, but are said to be recovering.

A massive explosion erupted at a natural gas pumping station outside of Nashville Tuesday after the station was apparently hit by one of the tornadoes, but no one was killed, a company spokesman said Wednesday. The blast shot flames hundreds of metres in the air and rattled windows for kilometres, witnesses said.

With files from the Associated Press