In central Illinois, residents were carefully sifting through debris in the "absolutely devastated" town of Fairdale - the scene of one of two tornadoes late Thursday.
"There's approximately 50 structures, and essentially every structure has sustained some damage" in Fairdale, said Matt Knott, fire chief in nearby Rockford, who sent most of his department to the town of about 200 people to help with the rescue. Some homes were leveled "down to the slabs," he said.
"This town is absolutely devastated," Knott said.
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At least one 67-year-old woman was killed in her home, according to DeKalb County Coroner Dennis Miller. At least seven other people with varying degrees of injuries were taken to hospitals. The town was not equipped with tornado sirens, Miller said.
The National Weather Service said Friday that storms damage survey teams "will be deployed to work with emergency management and assess the damage that has occurred."
Daniel Prothero, who encountered the scene as he was driving through the area, said, "It was horrible."
Power was shut off to Fairdale so search and rescue crews would be safe, said George Gaulrapp, a spokesman for Commonwealth Edison Co., who said, "It looks like a bomb went off."
"It's a tragedy," Gaulrapp said. "We just pray for the families."
One of the tornadoes destroyed a restaurant and flattened at least four houses in nearby Rochelle, authorities said. About a dozen people who were trapped in the restaurant's basement were believed to have been rescued safely, but fire crews were conducting a secondary search Thursday night. Any injuries were minor and didn't require ambulances, they said.
Police told NBC News there was also significant damage in the towns of Kings and Hillcrest. There was no immediate word on injuries there.
"This was a violent, long-track tornado," said Ari Sarsalari, a meteorologist for The Weather Channel.
More than 900 departures and arrivals were canceled at Chicago's O'Hare International Airport, and more than 950 others were delayed Thursday night.
The tornado was one of several that were spun off across Illinois and Iowa on the second day of a monster storm system that has peppered a 1,500-mile arc with grapefruit-size hail and winds up to 80 mph from Texas up to the Great Lakes and across to North Carolina.
On Friday, the front responsible for the severe weather was forecast to move south and east, threatening storms across the entire East Coast and Southeast.
"There will be the risk of thunderstorms pretty much from New York all the way down to the Gulf Coast," said Weather Channel lead meteorologist Brian Fortier. "There's a lot of lightning around."