UPDATE: US President Joe Biden has approved an emergency declaration for Kentucky after the state was battered by a swarm of tornadoes that have killed at least 100 people.
The devastating twisters ripped through six US states, leaving a trail of destroyed homes and businesses along a path that stretched more than 320km, officials said on Saturday.
Biden has ordered federal aid to supplement the response from state and local authorities, the White House said.
“It’s a tragedy. And we still don’t know how many lives were lost and the full extent of the damage,” Biden told reporters.
Kentucky Governor Andy Beshear said the collection of tornadoes was the most destructive in the state’s history.
He said about 40 workers had been rescued at the candle factory in the city of Mayfield, which had about 110 people inside when it was reduced to a pile of rubble.
It would be a “miracle” to find anyone else alive under the debris, he said.
“The devastation is unlike anything I have seen in my life and I have trouble putting it into words,” Beshear said at a press conference.
“It’s very likely going to be over 100 people lost here in Kentucky.”
Beshear said 189 National Guard personnel have been deployed to assist with the recovery.
The rescue efforts will focus in large part on Mayfield, home to some 10,000 people in the southwestern corner of the state where it converges with Illinois, Missouri and Arkansas.
Fire and police stations in Mayfield were destroyed, hindering the emergency response.
“We could feel the wind … then we did a little rock,” Kyanna Parsons-Perez, a worker at the candle factory, told NBC.
“And then boom everything came down on us.”
Mayfield Fire Chief Jeremy Creason, whose own station was destroyed, said the candle factory was diminished to a “pile of bent metal and steel and machinery” and that responders had to at times “crawl over casualties to get to live victims”.
Paige Tingle said she drove four hours to the site in the hope of finding her 52-year-old mother, Jill Monroe, who was working at the factory and was last heard from at 9.30pm.
“We don’t know how to feel, we are just trying to find her,” she said. “It’s a disaster here.”
The genesis of the tornado outbreak was a series of overnight thunderstorms, including a super cell storm that formed in northeast Arkansas.
The National Weather Service’s Storm Prediction Center said it received 36 reports of tornadoes touching down in Illinois, Kentucky, Tennessee, Missouri, Arkansas, and Mississippi.
One person was killed and five seriously injured when a tornado tore through a nursing home in Monette, Arkansas, while a few miles away in Leachville, Arkansas, a tornado destroyed a general store, killing one person, and laying waste to much of the city’s downtown.
“It really sounded like a train roaring through town,” the sheriff’s office said.
In Illinois, at least six workers were confirmed dead when an Amazon warehouse collapsed in the town of Edwardsville late on Friday.
Rescue workers were searching for people trapped in the rubble.
Drone footage showed a chaotic scene in the early morning dark, with many emergency vehicles around the area and rescuers with flashlights combing through debris.
The roof appeared to have been peeled back off the metal skeleton of the building.
In Tennessee, authorities said the severe weather killed at least three people.