Kentucky's governor says a devastating tornado touched down for 365km and dozens of deaths were feared in 10 counties.
Governor Andy Beshear said at a news conference Saturday that at least 70 people were feared dead in Kentucky, and the death toll could exceed 100.
"This will be, I believe, the deadliest tornado system to ever run through Kentucky," Beshear said.
Beshear said about 110 people were in a Mayfield candle factory hit by a tornado.
Local officials said national guard members and emergency workers from across the state were pouring into Mayfield to help with the search and rescue operation.
Kentucky State Police Trooper Sarah Burgess said search and rescue teams were going through the rubble on Saturday but didn't yet have a number for how many have died.
"We just can't confirm a number right now because we are still out there working, and we have so many agencies involved in helping us," Burgess said.
She said rescue crews were using heavy equipment to move rubble at the candle factory in western Kentucky. Coroners were called to the scene and bodies were recovered, but she didn't know how many. She said it could take a day and potentially longer to remove all of the rubble.
US President Joe Biden tweeted on Saturday that he was briefed on the situation and pledged the affected states would "have what they need as the search for survivors and damage assessments continue".
Kyana Parsons-Perez, an employee at the factory, was trapped under about 1.5m of debris for at least two hours until rescuers managed to free her.
In an interview with "Today," she said it was the "absolutely the most terrifying" event she had ever experienced.
"I did not think I was going to make it at all."
Just before the tornado struck, the building's lights flickered. She felt a gust of wind, her ears started "popping" and then: "Boom. Everything came down on us." People started screaming, and she heard Hispanic workers praying in Spanish.
Among those who helped rescue the trapped workers were inmates from the nearby Graves County Jail, she said.
"They could have used that moment to try to run away or anything, but they did not. They were there, helping us," she said. Elsewhere in Graves County, the landscape was a scene of devastation with uprooted trees, downed utility poles, a store destroyed and homes severely damaged.
At least one person died at an Amazon facility in Edwardsville, Illinois, Police Chief Mike Fillback told reporters on Saturday morning. The roof of the building was ripped off and a wall about the length of a football field collapsed.
Two people at the facility were taken by helicopter to hospitals in St Louis, Fillback said. The chief said he did not know their medical conditions. Edwardsville is about 40km east of St Louis.
It wasn't immediately clear whether the damage was caused by straight-line storms or a tornado, but the National Weather Service office near St Louis reported "radar-confirmed tornadoes" in the Edwardsville area around the time of the collapse.
About 30 people who were in the building were taken by bus to the police station in nearby Pontoon Beach for evaluation.
Early on Saturday, rescue crews were still sorting through the rubble. Fillback said the process could take several more hours. Cranes and backhoes were brought in to help move debris.
"The safety and wellbeing of our employees and partners is our top priority right now," Amazon spokesperson Richard Rocha said in a written statement Friday night. "We're assessing the situation and will share additional information when it's available."
Workers at a National Weather Service office had to take shelter as a tornado passed near their office in Weldon Spring, Missouri, 48km west of St Louis. One person died and two others were injured in building collapses near the towns of Defiance and New Melle, both just a few miles from the weather service office.
A tornado struck the Monette Manor nursing home in Arkansas on Friday night, killing one person and trapping 20 people inside as the building collapsed, Craighead County Judge Marvin Day told The Associated Press.
Five people had serious injuries, and a few others had minor ones, he said. The nursing home has 86 beds.
Three storm-related deaths were confirmed in Tennessee, said Dean Flener, spokesman for the Tennessee Emergency Management Agency. Two of the deaths occurred in Lake County, and the third was in Obion County — both in the northwestern corner of the state.
The storms swept through Bowling Green, Kentucky, near the Tennessee border, tearing off roofs of homes and flinging debris into roadways. The GM Corvette Assembly Plant and the nearby Corvette Museum sustained light damage. A semitrailer was overturned and pushed against a building just across the street.
Western Kentucky University's president said on Twitter one of its student who lived off-campus was killed. Timothy C Caboni, the school's president, offered condolences and asked all students to check in with loved ones. He said the school's main structures were mostly spared of major damage and that workers were trying to restore power, campus networks and phone lines.
The school called off commencement ceremonies that were planned for Saturday because the campus was without power.
Ronnie Ward, a Bowling Green police spokesman, said in a telephone interview that rescue efforts in Bowling Green and elsewhere were hampered by debris strewn across roads. Ward said numerous apartment complexes in Bowling Green had major structural damage, and some factories had collapsed during the storms.
"Right now we're focusing on the citizens, trying to get to everybody that needs us," Ward said.
Nearly 90% of Kraft Heinz products are already dye-free.