In Autauga County, Alabama, which is 66 kilometers northeast of Selma, at least six fatalities were confirmed and an estimated 40 to 50 homes were damaged or destroyed by storms that cut a strip across the county, said Ernie Baggett, the county's emergency management director.

At least 12 people were injured severely enough to be taken to hospitals by emergency responders, Baggett told The Associated Press, adding that he didn't know the extent of their injuries. He said crews were focused Thursday evening on cutting through downed trees to look for people who may need help.

"There are some houses that were completely destroyed that haven't been searched yet," Autauga County Coroner Buster Barber said late Thursday, adding that crews "are still in the process of searching through rubble."

In Georgia, a passenger died when a tree fell on a vehicle in Jackson during the storm, Butts County Coroner Lacey Prue said. In the same county southeast of Atlanta, the storm appeared to have knocked a freight train off its tracks, officials said.

Nationwide, there were 33 separate tornado reports Thursday from the National Weather Service as of Thursday evening, with a handful of tornado warnings still in effect in Georgia, South Carolina and North Carolina. However, the reports were not yet confirmed and some of them could later be classified as wind damage after assessments are done in coming days.

In Selma, a city etched in the history of the civil rights movement, brick buildings collapsed, cars were on their side and traffic poles were strewn about in the downtown area. Plumes of thick, black smoke rose over the city from a fire burning. It wasn't immediately known whether the storm caused the blaze.

A few blocks past the city's famed Edmund Pettus Bridge, an enduring symbol of the voting rights movement, buildings were crumpled by the storm and trees blocked roadways.

Selma Mayor James Perkins said no fatalities have been reported, but first responders were continuing to assess the damage.

"We have a lot of downed power lines," he said. "There is a lot of danger on the streets."

A city of about 18,000 residents, Selma is about 80 kilometers west of the Alabama capital city of Montgomery. It was a flashpoint of the civil rights movement and where Alabama state troopers viciously attacked Black people advocating for voting rights as they marched across the Edmund Pettus Bridge on March 7, 1965.

After the tornado passed, Krishun Moore emerged from her home to the sound of children crying and screaming. She and her mother encouraged the kids to keep screaming until they found the two of them on top of the roof of a damaged apartment. She estimated the kids were about 1 and 4 years old. Both of them are OK, she said through Facebook messenger.

Malesha McVay drove parallel to the tornado with her family. She said it got less than 2 kilometers from her home before suddenly turning.

"We stopped and we prayed. We followed it and prayed," she said. "It was a 100 per cent God thing that it turned right before it hit my house."

She took video of the giant twister, which would turn black as it swept away home after home.

"It would hit a house, and black smoke would swirl up," she said. "It was very terrifying."

Former state Senator Hank Sanders said the twister "hit our house, but not head-on."

"It blew out windows in the bedroom and in the living room," he said. "It is raining through the roof in the kitchen."

About 40,000 customers were without power in Alabama on Thursday night, according to PowerOutage.us, which tracks outages nationwide. In Georgia, about 86,000 customers were without electricity after the storm system carved a path across a tier of counties just south of Atlanta.

The storm hit in Griffin, south of Atlanta, with winds damaging a shopping area, local news outlets reported. A Hobby Lobby store partially lost its roof, and at least one car was flipped in the parking lot of a nearby Walmart.

Damage was also reported west of downtown Atlanta in Douglas County and Cobb County, with Cobb County government posting a damage report showing a crumbled cinder block wall at a warehouse in suburban Austell.

In Kentucky, the National Weather Service in Louisville confirmed that an EF-1 tornado struck Mercer County and said crews were surveying damage in a handful of other counties.

Three factors — a natural La Nina weather cycle, warming of the Gulf of Mexico likely related to climate change and a decades-long shift of tornadoes from the west to east — came together to make Thursday's tornado outbreak unusual and damaging, said Victor Gensini, a meteorology professor at Northern Illinois University who studies tornado trends.

The La Nina, a cooling of parts of the Pacific that changes weather worldwide, was a factor in making a wavy jet stream that brought a cold front through, Gensini said. But that's not enough for a tornado outbreak. What's needed is moisture.

Normally the air in the Southeast is fairly dry this time of year but the dew point was twice what is normal, likely because of unusually warm water in the Gulf of Mexico, which is likely influenced by climate change. That moisture hit the cold front and everything was in place, Gensini said.?