At least 44 people are dead after more than 240 tornadoes swept through the southern United States over the weekend, leaving a path of destruction in their wake.

Residents in the Carolinas, Arkansas, Mississippi, Alabama and Oklahoma are searching for survivors and assessing the damage Monday, a ritual that has become too common for many who have experienced this kind of destruction before.

The state of North Carolina was hardest hit, with at least 21 people killed there alone. The storm, which sparked flash floods and hail as big as grapefruits, caused significant damage in at least 26 counties and knocked out power to more than 200,000 people.

Things were particularly frightening for shoppers in a Sanford, N.C. Lowe's store, who erupted into a collective panic after a tornado pulled off the building's steel roof on Saturday. None of the 100 people there at the time were badly injured.

Gov. Beverly Perdue said the storm was North Carolina's deadliest in two decades as she declared a state of emergency late Sunday.

The 62 tornadoes reported in North Carolina were three times the number of twisters the state usually gets all season. They were also the deadliest since March 1984, when 22 twisters hit the Carolinas killing 42 in North Carolina and injuring hundreds more.

"We're beginning to recover from what we believe is the most widespread tornadoes we've seen since the mid-80s," Perdue told reporters.

The storm raked across both cities and remote rural communities, lifting homes off their foundations and pitching cars around like sticks. Perdue said the devastation she saw Sunday left her near tears.

The governor said she'd been in contact with U.S. 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."

Storm chaser and filmmaker George Kourounis says it's rare enough for tornadoes to hit North Carolina, but it's rarer still for them to hit this early in the spring.

"Every year the U.S. gets between 800 and 1,000 tornadoes, but typically not this many this early," he told Canada AM Monday morning.

The conditions that typically occur along the plains of "tornado alley," which cuts straight through the middle of the country, almost never happen as far east as North Carolina, Kourounis noted.

"This was a very powerful that tracked across the U.S. for three days, spreading tornados from Oklahoma to the East Coast."

The violent weather began Thursday in Oklahoma, where two people died, before cutting across the Deep South on Friday and hitting North Carolina and Virginia on Saturday.

Seven people died in Arkansas; seven in Alabama; six in Virginia; and one in Mississippi.

As is so often the case with tornadoes, many of the deaths occurred in mobile homes. U.S. census data estimates that 14.5 per cent of residences in North Carolina are mobile homes – one of the highest percentages.

With files from The Associated Press