Survivors of one of the deadliest swarms of twisters in U.S. history are combing through the rubble of their broken homes Friday, trying to figure out how to put their lives back together.

At least 328 people were killed across six states as more than 160 tornadoes tore through the southern U.S., causing billions of dollars in damage. It's being described as the worst natural disaster in the U.S. since Hurricane Katrina in 2005.

Alabama was by far the most badly hit state. More than two-thirds of those killed lived in there, where twisters two kilometres wide seemed to target the most populated areas.

Alabama emergency management officials said in a news release early Friday that not only were 238 Alabamans killed in the afternoon storms, hundreds more were injured, including 800 in the badly hit town of Tuscaloosa, home to the University of Alabama.

There were also deaths in Mississippi, Tennessee, Georgia, Virginia and Kentucky. The tornadoes killed more people than any other storm system since April 1974, when 315 people were killed by twisters in 13 Southern and Midwestern states.

As many as a million homes and businesses in the destruction zone were without power, and 2,000 National Guard troops are now on the ground in Alabama to help clear roads and restore power.

Survivors of the storms told stories of finding makeshift shelter in the final minutes before the twisters raked over their homes.

Victoria Mattox, 29, a teacher n Barnesville, Ga., told The Associated Press she was sleeping when a friend texted her at 12:42 a.m. Thursday to tell her sirens were going off in town. She leapt from bed and ran into her closet.

Seconds later she could feel her house shaking under battering winds. Windows popped out in the adjoining bedroom and then the ceiling peeled off above her head.

Within seconds, it was over and the closet where she had chosen was the only part of the house left standing. A large tree had been uprooted and arched over her as she stepped out of the closet.

A Georgia salon owner, Lisa Rice, and her two daughters, 19-year-old Stormy and 21-year-old Sky, said they climbed inside a tanning bed while a tornado ripped the roof off their store. Somehow, the sturdy tanning bed saved them.

"Sky said, 'We're going to die.' But, I said, 'No, just pray. Just pray, just pray, just pray,"' Lisa Rice said.

For 30 seconds, wind rushed around the bed and debris flew.

"Then it just stopped. It got real quiet. We waited a few minutes and then opened up the bed and we saw daylight," she said.

Police are now trying to deal with survivors who want to return to their homes to recover belongings, despite the dangers posed by the downed power lines and debris. Some residents ducked police roadblocks and fallen trees even as police used bullhorns to warn them to stay back.

The town of Tuscaloosa has now imposed a 10 p.m. curfew for Thursday and an 8 p.m. limit for Friday.

Concord, a small town outside Birmingham, was so devastated that authorities closed it down to keep out looters and gawkers.

U.S. President Barack Obama planned a trip to Tuscaloosa on Friday to view the damage and meet Alabama Gov. Robert Bentley.

Late Thursday, Obama, who called the damage to homes and businesses in the hardest-hit state of Alabama "nothing short of catastrophic," signed a disaster declaration for the state to provide federal aid to those who seek it.

"We can't control when or where a terrible storm may strike, but we can control how we respond to it," Obama said.

"And I want every American who has been affected by this disaster to know that the federal government will do everything we can to help you recover and we will stand with you as you rebuild."