MAYFIELD, KENTUCKY (REUTERS, AFP) - On the day before Thanksgiving, Mayfield Consumer Products in western Kentucky posted photos online showing smiling employees lining up at a buffet table ready to enjoy a special pre-holiday meal together in the factory canteen.

On Friday night, the candle-making plant where workers had celebrated two weeks earlier lay in ruins, flattened by a devastating tornado during a late shift as more than 100 employees toiled inside. The next morning, 40 of them had been rescued; many of the rest were missing.

The destruction came as dozens of devastating tornadoes roared through five US states overnight, leaving more than 80 people dead Saturday (Dec 11) in what President Joe Biden said was "one of the largest" storm outbreaks in history.

Search-and-rescue teams on Saturday combed through the debris of the tornado-ravaged factory on the west side of Mayfield, a picturesque town near the confluence of the Ohio and Mississippi rivers in the far southwestern corner of Kentucky.

Mayfield, a community of about 10,000 residents in Graves County, was transformed by the tornado into a landscape cluttered with damaged and demolished buildings, strewn debris, trees uprooted and stripped bare, twisted road signs and sagging utility lines.

Among those said to be unaccounted for at the wrecked candle-making factory was an employee identified by family as Ms Jill Monroe, 52, who was last heard from at 9.30pm, around the time the storm struck, according to her daughter, Ms Paige Tingle.

Reached through Facebook on Saturday, Ms Tingle told Reuters she had driven four hours to the factory site in the hopes of finding her mother, whose fate remains unknown.

"We don't know what to think. We are extremely nervous. We don't know how to feel, we are just trying to find her," Ms Tingle said. "It's a disaster here. My thoughts go out to everyone."

One employee, who survived the collapse, live streamed a video from inside where she was trapped, her legs pinned under the rubble.

"I'm really scared," Ms Kyanna Parsons-Perez can be heard saying in a live video she shared on Facebook while she waited to be rescued.

The screams and prayers of other workers, some in Spanish, pierce the almost complete darkness of the collapsed factory.

"I didn't think I was going to make it," Ms Parsons-Perez said in another video she shared after her rescue on Saturday, her birthday.

"My legs, I couldn't move them and I was just freaking out," she said, calling the experience the scariest of her life.

There were no immediate casualty estimates available for the factory or the surrounding community, one of the hardest-hit areas of a storm that carved a 322km-long path of destruction through several counties.

But Governor Andy Beshear estimated at least 100 people had perished in Kentucky as a whole.

About 110 people were believed to have been inside the candle-making plant when it was levelled by the twister, with 40 people rescued as of Saturday afternoon, Mr Beshear told reporters at a news conference.

The Graves County coroner earlier told CNN that 40 people remained unaccounted for at the factory.

"This event is the worst, most devastating, most deadly tornado event in Kentucky's history," said Mr Beshear.

"The devastation is unlike anything I have seen in my life, and I have trouble putting it into words," he told reporters. The western Kentucky town of Mayfield was reduced to "matchsticks," its mayor said.

Besides those killed in Kentucky at least six died in an Amazon warehouse in Illinois where they were on the night shift processing orders ahead of Christmas.

"It's a tragedy," a shaken Mr Biden said in televised comments.

"And we still don't know how many lives are lost and the full extent of the damage."

As darkness fell Saturday, scores of search and rescue officials were helping stunned citizens across Arkansas, Illinois, Kentucky, Missouri and Tennessee to sift through the rubble of their homes and businesses searching for any more survivors.

In one demonstration of the storms' awesome power, winds derailed a 27-car train near Earlington, Kentucky, one car was blown nearly 70m up a hill and another landed on a house. No one was hurt.

Reports put the total number of tornadoes across the region at around 30.

At least 13 people were killed in other storm-hit states, including at the Amazon warehouse in Illinois.

Scientists have warned that climate change is making storms more powerful and frequent.

Mr Biden said that while the impact on these particular storms was not yet clear, "we all know everything is more intense when the climate is warming, everything".

The American Red Cross said it was working to provide relief across all five states.

More than half a million homes in several states were left without power, according to PowerOutage.com.