Authorities said they had little hope of finding survivors after the tornadoes tore through the US Midwest and South on Friday night, killing people in at least five states.
Six workers died at an Amazon warehouse in Illinois, while a nursing home was struck in Arkansas.
"To the people of America, there is no lens big enough to show you the extent of the damage," Kentucky Governor Andy Beshear told reporters on Sunday evening, saying one tornado tore across 365km of terrain.
The governor said at least 80 people in his state were confirmed dead and the toll was eventually going to exceed 100.
"We're still hoping as we move forward for some miracles," Beshear said.
Nowhere suffered as much as the small town of Mayfield, Kentucky, where the large twisters - unusual in winter - destroyed a candle factory along with the fire and police stations.
Across the community of 10,000 people in the state's southwestern corner, homes were flattened or missing roofs, giant trees had been uprooted and street signs were mangled.
Laurie Lopez, 53, received a tornado alert on her phone about 20 minutes before her house started shaking. She took cover in a hallway with her 19-year-old daughter and their two dogs.
"Soon the (window) glass started just bursting in, we could hear it flying. I have it all over my bedroom," she said, adding the tornado "sounded like a freight train going through a brick house".
Steve Wright, 61, was driving around looking for petrol on Sunday morning. A resident of Mayfield for the last four years, his apartment complex was largely spared.
After the storm had passed, he took a torch and walked around town looking for people who might be trapped. He ended up helping a father pull his dead three-year-old from the rubble.
"It was bad. I helped dig out a dead baby, right up here," he said gesturing to debris that used to be a two-storey house.
"I prayed for both of them, that was all I could do."
Beshear said the tornadoes were the most destructive in the state's history and knocked out power to between 36,000 and 50,000 homes.
More than 300 members of the National Guard were going door to door and removing debris, while teams were working to distribute water and generators.
In Edwardsville, Illinois, six Amazon workers were killed and more were missing after the plant buckled under the force of the tornado.
The genesis of the tornado outbreak was a series of overnight thunderstorms, including a super cell storm that formed in northeast Arkansas and moved into Arkansas and Missouri and then into Tennessee and Kentucky.
Deanne Criswell, administrator of the US Federal Emergency Management Agency, called the magnitude of the tornadoes "historic".
The agency was opening shelters and sending teams and supplies, including 30,000 meals and 45,000 litres of water, she said.
Speaking at a press conference on Sunday she said Governorn Beshear had formally asked the federal government to declare a major federal disaster, allowing for the release of additional resources.
US President Joe Biden on Saturday declared the tornadoes that hit Kentucky a federal emergency and pledged support for all the affected states.
