Several states began the arduous cleanup process Monday after 240 tornadoes touched down across the United States over the weekend, killing at least 44 people.

The death toll across Oklahoma, Arkansas, Mississippi, Alabama and the Carolinas stands at 44 after the region experienced some of the worst storms in decades. More than 60 tornadoes touched down in North Carolina alone, although officials say some storms may have been reported more than once.

One apparent twister passed near a Virginia nuclear power plant, knocking down power lines. Dominion Virginia Power said backup sources including diesel generators kept electricity going to maintain both units at its Surry Power Station. The tornado didn't hit the two nuclear units, which are designed to withstand such calamities as earthquakes and hurricanes, the company said.

More than 100 employees and customers screamed in near unison when the steel roof was peeled off a Lowe's store in Sanford, N.C., on Saturday. The store became part of the wreckage left by a ferocious storm system bristling with killer twisters that ripped through the South.


A man cuts down a tree in Raleigh, N.C., after tornadoes tore through the Carolinas over the weekend. ((Chris Keane/Reuters))

"You could hear all the steel ripping, people screaming in fear for their lives," manager Michael Hollowell told The Associated Press on Sunday.

No one at the store was killed.

A state of emergency remains in effect for all of Virginia and South Carolina, and parts of four other states.

In all of Lee County, where Sanford is located, about 60 kilometres south of Raleigh, there was just one confirmed death from the storm, which claimed at least 21 lives statewide, damaged hundreds of homes and left a swath of destruction unmatched by any spring storm since the mid-1980s.

In Raleigh early Monday, authorities were blocking access to a mobile home park of about 200 homes where three children were killed. Officials planned to assess conditions after sunrise before deciding whether to allow residents to return home.

Power lines and trees still covered nearby roads. Where roads were clear, there were massive piles of debris that had been pushed to the side of the street.

Although it will take weeks to tally the damage, the violent weather system is likely to rank among the largest in history. It is already the deadliest since the storms that hit numerous states on Super Tuesday in 2008.

Survivors were left to recall miraculous escapes.

In the Bladen County community of Ammon, about 110 kilometres south of Raleigh, Audrey McKoy and her husband Milton saw a tornado bearing down on them over the tops of the pine trees that surround the seven or eight mobile homes that make up their neighbourhood. He glanced at a nearby farm and saw the winds lifting pigs and other animals in the sky.

"It looked just like The Wizard of Oz," Audrey said.

They took shelter in their laundry room and, after emerging once the storm had passed, were disoriented for a moment. The twister had turned their mobile home around and they were standing in their backyard.

Milton found three bodies in their neighbourhood, including 92-year-old Marchester Avery and his 50-year-old son, Tony, who died in adjacent mobile homes. He stopped his wife from coming over to see.

"You don't want to look at this," he told her.

The storms crushed trailer parks and brought life in the centre of the state's second-largest city to a virtual standstill. It was the worst outbreak in the state since 22 twisters in 1984 killed 42 people.

Obama pledges support

North Carolina Gov. Beverly Perdue planned to tour hard-hit areas in three counties Monday. The devastation she saw Sunday left her near tears, she said. The storm pummelled bustling cities and remote rural communities. One of Perdue's stops was downtown Raleigh, where fallen trees blocked major thoroughfares and damage to the Shaw University campus forced it to cancel the remainder of its spring semester.

Perdue said that she'd been in contact with President Barack Obama, who pledged his support, and that federal emergency management workers were already on the ground.

"We have in North Carolina a tremendous relationship with our federal partners and have been through this so many times," she said. "That's not a good thing. That's a bad thing."


Residents look at a tree that fell into a home in Raleigh, N.C., over the weekend. ((Chris Keane/Reuters))

The conditions that allowed for the storm occur on the Great Plains a few times a year on average but almost never happen in North Carolina.

This time of the year the contrast between air masses across North America is tremendous, CBC meteorologist Johanna Wagstaffe said. Cool, dry air to the north collides with warm, humid air to the south, with the collision path occurring right over the Mississippi Valley in this case.

The atmosphere was unstable Saturday, which allowed air to rise and fall quickly, creating winds of hurricane strength or greater. There was also plenty of moisture in the air, which fuelled violent storms. Shear winds at different heights, moving in different directions, created the spin needed to create tornadoes, Sharp said.

Many of the deaths across the state occurred in mobile homes like the ones in Ammon. The three deaths in Raleigh were in a mobile home park about eight kilometres north of downtown, which was still closed off to residents early Monday.

Census data from 2007, the latest available, estimates 14.5 per cent of residences in North Carolina are mobile homes, the seventh highest percentage in the U.S. and well over the national average of 6.7 per cent.

North Carolina officials tallied more than 130 serious injuries, 65 homes destroyed and another 600 significantly damaged by Sunday evening, according to state public safety spokeswoman Julia Jarema. Officials expect those totals to climb as damage assessments continue.

Back at the Lowe's store, Joseph Rosser and his 13-year-old daughter, Hannah, had pulled their Chevrolet Colorado pickup off the road Saturday, seeking shelter. Instead, the store's exterior concrete toppled, crushing the truck's cab with Rosser and Hannah inside.

Thought he was dying

"I really didn't see much because I had a pillow over my face to protect my head and I heard my dad tell me it was going to be OK," said Hannah, her midsection wrapped in a back brace. "And then all of a sudden, I just heard a loud boom.

"My dad was lying there, telling me he was going to die. He sounded very hoarse like he couldn't breathe. He was crying and was hurt really bad."

She crawled out the truck's shattered back window and ran around the parking lot calling for help, because her cellphone wouldn't work. Both Rossers are recovering from their injuries.

Residents and officials alike are looking to make repairs and start building what was lost.

Aleta Tootle and four other people took shelter in a closet in her Bertie County home, emerging with only a few scratches after the rest of the building was ripped to shreds. Surveying the wreckage Sunday, she said there was only one thing left to do.

"All we can do is start over," she said. "We don't have a choice."

With files from The Associated Press