Birmingham: Deadly tornados and flash floods flattened buildings and overturned vehicles overnight on Thursday as a major storm tore through the United States, its death toll rising to nearly 80 people.
Forty-five people were killed in Alabama alone, authorities said, and President Barack Obama said Washington would be rushing search and rescue assistance to the southeastern state.
States of emergency were declared in Alabama, Arkansas, Kentucky, Mississippi, Missouri, Tennessee and Oklahoma, and governors called out the National Guard to help with rescue and cleanup operations.
The National Weather Service had preliminary reports of nearly 300 tornados since the storm began on Friday, including more than 130 on Wednesday alone.
Alabama was especially badly hit, caught by two lines of storms that killed at least 25 people over 24 hours, Yasamie August with the Alabama Emergency Management Agency (EMA) said.
An evening tornado tore through the city of Tuscaloosa, home to the University of Alabama, and the city "has been majorly impacted”, August said.
"We`re still trying to assess how bad the damage is," said August, adding that the local EMA office was among the buildings struck.
Tuscaloosa Mayor Walter Maddox told CNN that the tornado had "obliterated blocks and blocks" of his city.
"My wife and I were watching the weather coverage until the monster was right up on us," Tuscaloosa resident Will Nevin told The Birmingham News, the local newspaper.
"Then it was the mad dash to the bathroom where the lights flickered, pulsed and finally gave up."
A tornado also struck the city of Birmingham and officials were still assessing the damage, August said.
"This has been a very serious and deadly event that`s affected our state, and it`s not over yet," Alabama Governor Robert Brantley told reporters after the second string of storms.
It issued a rare "high-risk" warning of tornados, hail, flash flooding and dangerous lightning for parts of Alabama, Georgia and Mississippi.
It warned that severe weather could also strike 21 states from the Great Lakes down to the Gulf Coast and across to the Atlantic.
Tornados were reported as far east as Virginia and Maryland, where they touched down near Washington, DC without injuring anyone.
Storm victims across the region were trapped in homes, trailers and cars by falling trees. Hail the size of golf balls cracked windows.
Roads were washed out or rendered impassable by fallen trees and power lines across the region. Homes, schools and businesses were flattened, flooded and set on fire by lightning.
"Our citizens have endured days of consecutive severe storms and flooding," said Kentucky Governor Steve Beshear.
"We stand ready to assist any community in need, and we urge Kentuckians to remain on alert until this storm system finally passes."
Hundreds of people were evacuated from their homes in Missouri after levees failed to hold back swollen rivers.
"I`m just glad my family is safe," said Chris Pigg, who spent the night at a shelter with his wife and daughter and wasn`t sure if he`d have a home to return to after the Black River breached the levee in Poplar Bluff, Missouri.
The death toll was set to rise as skies are not expected to clear until late Thursday or Friday, and there will be little time to mop up, as another major storm system is forecast to bring heavy rain and high winds on Saturday.
The storms come after a wet spring and a winter of heavy snowfall which left the ground saturated and rivers running high.
Officials were considering deliberately destroying levees in some areas to ease pressure on swollen rivers, some of which are so high that barges have become trapped under bridges.
As much as 18 inches (45 centimetres) of rain had fallen from Saturday through Tuesday night in some areas.
"It`s producing major to record flooding in a lot of those river basins," said Jim Keeney, deputy chief of the weather service`s central region.
State officials reported 11 deaths each in Mississippi and Arkansas, and a spokeswoman for Georgia`s emergency management agency said nine people died on Wednesday as a result of the storms.
Another three deaths were reported in Missouri and Tennessee.
"There`s trees down, the power`s down, you`ve got homes that are damaged... as well as a lot of flooding going on," Renee Preslar, a spokeswoman for the Arkansas department of emergency management, said.
Officials across the country begged people to use common sense and not to try to drive or walk through the floodwater.
"Some people are still trying to drive around barricades with their cars. Please don`t do that," Louisville, Kentucky Mayor Greg Fisher said at a press conference.
"If it`s moving fast you can go with it."