President Joe Biden on Monday declared a major federal disaster in Kentucky, paving the way for additional federal aid, the White House said.
Officials had said the death toll could soar past 100 from twisters that tore through at least six states in the US Midwest and South on Friday night, while seeing little chance of finding survivors in the rubble two days on.
In Kentucky, Governor Andy Beshear estimated the death toll at 80 and said it was certain to rise above 100, but that was based on suspicion that scores were killed when a candle factory was destroyed in the small city of Mayfield.
Up to 70 people at the factory had been believed dead, but that number could be revised down to 16 or fewer, a company spokesman said, raising the possibility the governor's death toll estimate could come down significantly.
Among the 110 people who were at the factory, eight have been confirmed dead and eight were missing, said Bob Ferguson, a spokesperson for Mayfield Consumer Products.
"There were some early reports that as many as 70 could be dead in the factory. One is too many, but we thank God that the number is turning out to be far, far fewer," Ferguson told Reuters, adding that rescue teams were still searching for the eight who remained unaccounted for.
It was unclear how many factory workers Beshear was counting in his estimated death toll, which he formulated on Saturday and said on Sunday remained unchanged - at least for now.
"We're still getting information in on the candle factory. The owner has been in contact and believes he has some different information. We are trying to verify it. If so, it may be a better situation and the miracle we were hoping for," Beshear told a news conference earlier on Sunday evening.
Dakota Moore, 20, was working at the candle factory when the tornado warning came. As was the drill, everyone – about 100 people - lined up in the hallway in the centre of the building, near the bathrooms.
"My ears started ringing. I started looking around and everybody down on the other side by the women's bathroom started ducking down. The walls started coming in on that side. There was this old lady, I was trying to get to her, and the wall took me down," Moore said.
He said he tried to help another man who was stuck in rubble up to his neck, but was unable to lift him out.
"I was able to get to his neck to see if he had a pulse or anything. Flatline," he said.
Rescue workers continue to scour debris for survivors and many people without power, water or even a roof over their heads salvaged what they could.
While Kentucky was hardest hit, six workers were killed at an Amazon.com Inc warehouse in Illinois after the plant buckled under the force of the tornado.
A nursing home was struck in Arkansas, causing one of that state's two deaths. Four were reported dead in Tennessee and two in Missouri.
Nowhere suffered as much as Mayfield, a community of about 10,000 in the southwestern corner of Kentucky, where the large twisters also destroyed the fire and police stations.
The governor said the tornadoes were the most destructive in the state's history and that even the sturdiest structures of steel and brick were flattened. One twister tore across 365km of terrain.
Biden told reporters he would ask the Environmental Protection Agency to examine what role climate change may have played in fueling the storms.
The US Federal Emergency Management Agency was opening shelters and sending teams and supplies.
