Storms unleashed devastating tornadoes late Friday and early Saturday across parts of the central and southern United States, collapsing buildings into twisted debris and claiming lives, with officials fearing the death toll could exceed 80.
In Kentucky alone, the state's governor says more than 70 people could have died after "one of the toughest nights in Kentucky history".
Tornadoes or strong winds collapsed an occupied candle factory in Kentucky, an Amazon warehouse in western Illinois, and a nursing home in Arkansas, killing people in each community and leaving responders scrambling to rescue others.
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More than 30 tornadoes have been reported in at least six states, including Missouri, Tennessee and Mississippi.
A stretch of more than 402 kilometres from Arkansas to Kentucky might have been hit by one violent, long-track twister, CNN meteorologists say.
"I'm pretty sure that number (killed in Kentucky) is north of 70 … it may, in fact, exceed 100 before the day is done," Kentucky Gov. Andy Beshear said late on Saturday morning.
"The level of devastation is unlike anything I have ever seen."
One of the most devastated sites is the southwestern Kentucky city of Mayfield, where a tornado hit the Mayfield Consumer Products candle factory on Friday night while people were working.
About 110 people were inside and dozens are feared dead there, Mr Beshear said.
"They rescued 40," Mr Beshear said at a news conference on Saturday afternoon.
"There's at least 15 feet of metal with cars on top of it, barrels of corrosive chemicals that are there, it will be a miracle if anybody else is found alive in it."
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The governor said he also visited Dawson Springs, his father's hometown, with a population of about 2700 where he says: "they're going to lose a whole lot of people."
"One block from my grandparent's house, there's no house standing and we don't know where all those people are," Mr Beshear said.
Video from Mayfield showed what remained of the factory there: a massive debris field, largely of twisted metal, several feet high, with rescuers using hands and machines to dig through.
Among the survivors were Kyanna Parsons-Perez, who said workers had been hustled to a safety area before the storm hit.
While attendance was being taken, she saw "a little dust of wind".
"My ears start popping. And it was like the building, we all just rocked back and forth, and then boom – everything fell on us," Kyanna Parsons-Perez told CNN's Boris Sanchez.
Pinned by debris with others, she used her phone to broadcast on Facebook Live and called 911, her mother and a coworker's relative.
She knew rescuers were around only when she could feel pressure from above – people walking on the debris.
"I was screaming like, 'Sir, can you please just get this so I can move my leg?'
He said, 'Ma'am, there's about five feet worth of debris on top of you,'" she said.
Rescuers eventually pulled her and others out, she said.
An official Kentucky death toll hasn't been released; deaths have been reported in Arkansas (two), Tennessee (four), Illinois (six) and Missouri (two).
In Warren County, Kentucky, children are among 12 storm-related fatalities, the county coroner's office confirmed to CNN on Saturday afternoon.
Warren County Coroner Kevin Kirby said that most of the fatalities are from the Russellville Road area.
The National Guard and other Kentucky state personnel are deploying to hard-hit areas for "house-to-house" searches and debris removal, Mr Beshear told CNN.
"I want to thank every local emergency management employee, police officer, firefighter and first responder," he said.
"This has been one of the toughest nights in Kentucky history. It's hard to put into words.
"Remember, each of these lost lives are children of God, irreplaceable to their families and communities.
"But we will make it through this. We will rebuild. We are strong, resilient people and we're going to be there every step of the way. This is one state standing strong."
He declared a state of emergency.
Biden to travel to damaged region
President Joe Biden told reporters traveling with him in Wilmington, Delaware on Saturday he had been closely monitoring the situation and had called the governors of the states that had been severely impacted by one of the "largest tornado outbreaks in our history".
"I want to emphasise what I told all the governors, the federal government will do everything, everything you can possibly do to help," he said, adding that he'd deploy the National Guard to states that deemed it necessary.
Mr Biden told reporters he plans to travel to the region to survey storm damage when circumstances allow but didn't want to be in the way.
"When a president shows up, he shows up with an awful lot of personnel, an awful lot of vehicles, an awful lot of – we can get in the way, unintentionally.
"And so, I'm working with the governor of Kentucky and others who may want me to be there, I made sure that we're a value-added at the time, and we're not going to get in the way of the rescue and recovery, but I do plan on going.
"My heart aches for those people right now, including the rescuers, including the burden on them and what they worry about.
"I just think that we just have to keep at it. We have to keep focused. And this is going to be the focus of my attention until we get this finished."
In an earlier message on Twitter, Mr Biden called losing a loved one in storms like this an "unimaginable tragedy".
He said he had spoken with Mr Beshear and "indicated that he has directed FEMA and other federal agencies to provide the speediest assistance possible to impacted communities," the White House said.
The White House later said Biden had approved a federal emergency declaration for Kentucky.
'Many, many' people pulled from Kentucky factory
Ivy Williams was at the Mayfield site on Saturday, looking for his wife of 30-plus years, who he says was at the factory.
"I hope she's somewhere safe," Ms Williams said, through tears.
"Please call me … I'm looking for you, baby."
First responders have pulled "many, many" people out of the rubble, some alive and some apparently dead, storm chaser Michael Gordon told CNN Saturday morning from the scene.
"It's kind of hard to talk about. … They're digging in that rubble by hand right now," Mr Gordon said.
Graves County, Kentucky, Commissioner Todd Hayden told CNN's Pamela Brown he arrived at the candle factory in the dark to find "nothing but a pile of rubble".
"You wondered how anybody could still be alive in there. Knowing there were a lot of people in that place, a bunch of us went over and started trying to uncover what might be there," Mr Hayden said.
"Seeing people come out of that pile of rubble alive was just amazing.
"We would send in sawzalls and cutting tools to cut wires and bars and then all of a sudden they would come up out of a hole."
Mr Hayden said they probably rescued 10-12 people from the part of the debris where he was, some injured and many stunned and in shock.
"Some of them would come out crying. They'd see their husband or their father or whatever and they would immediately go to their arms and just fall in them. Other people – one lady came out she was kind of dancing, she was so happy to be out of there."
People were working at the factory as it has been "going 24/7" in part to meet Christmastime candle demand, US Rep. James Comer, who represents the area, told CNN.
Graves County Coroner Brad Jones told CNN that "about 40" people remained unaccounted for at the factory.
He declined to say how many of the more than 100 workers at the workspace had been accounted for.
Other buildings hit in Mayfield, a city of around 10,000 people, include the Graves County courthouse and adjoining jail.
"It's changed the landscape … here in Mayfield," Kentucky State Police Lt. Dean Patterson said.
"We're seeing (destruction) that none of us have ever seen before."
On Saturday afternoon, Mr Patterson described to CNN the process being used to try to find survivors in the town.
"It's a very thorough and slow process, because you have to be careful when you are dealing with so much debris, and so many unknowns," he said.
"One wrong move and you could actually cause more damage, so it's a slow methodical process.
"Lots of people out there, working together to do everything they can to hopefully find some survivors in that devastating area."
Mr Patterson said that overnight emergency workers had received "dozens if not hundreds" of calls from people trying to find out if their loved ones were alright.
Once the sun rose, troopers went to the addresses flagged to them to try to make contact and let concerned relatives know, he said.
"We are still doing that right now, we're doing welfare checks and basically going door-to-door or what used to be a door to make sure there is no one else inside."
Graves County jailer George Workman told CNN that his main jail is in ruins and he was forced to evacuate the 83 inmates to other facilities because the damage was so severe. None were injured at the jail when the tornado hit.
"(The damage is) structurally bad enough that I question it'll ever be able to open again," Mr Workman said.
Mr Workman said one of his deputies on assignment at the candle factory was killed when the tornado hit.
The deputy was at the factory as part of a work-release program for low-security, low-level offenders that had just started last week.
Seven inmates were also on-site at the factory; three of them were treated for injuries at the scene.
Kyanna Parsons-Perez, who was trapped under at least five feet of rubble, told CNN that those inmates helped rescue her and others from the rubble.
A hospital in Paducah, Kentucky, some 43 kilometres north of Mayfield, has been treating tornado victims, a spokesperson told CNN.
A majority of those being treated had chemical burns, long bone injuries and crush injuries, Mercy Health Lourdes Hospital spokesperson Nanette Bentley said.
National Weather Service Chief Meteorologist John Gordon told a news conference in Kentucky that the tornado event was a "worst-case scenario".
"Warm air in the cold season, middle of the night – this sickens me to see what has happened," he said.
"Look at the pictures on your screens. Homes, totally impaled, two-by-fours through cars, eighteen-wheelers thrown 30 feet moved in the northwesterly direction – that takes a lot of force."
Severe thunderstorms still are possible Saturday from the northern Gulf states into the south-central Appalachians, the National Weather Service's Storm Prediction Center said.
Tornado watches throughout the region were expected.
