The tornado, estimated to have winds of at least 158 mph, hit a horse track near Henderson, Ky., then jumped the Ohio River into Indiana around 2 a.m.
"It was just a real loud roar. It didn't seem like it lasted over 45 seconds to a minute, then it was calm again," said Steve Gaiser, who lives near the Eastbrook Mobile Home Park in Evansville.
CBS News correspondent Cynthia Bowers reports that although the tornado left a 20 mile path of destruction, ground zero was the mobile home park, where late Sunday rescuers were still digging through debris, searching for survivors.
At least 17 people were killed in the mobile home park, according to Eric Williams of the Vanderburgh County Sheriff's Department.
More people were believed to still be trapped in the debris, and National Guard units were called in to help with search-and-recovery efforts. At least 200 people were injured during the storm.
"They were in trailer homes, homes that were just torn apart by the storm, so they're just now getting in there trying to find people," said deputy Vanderburgh county coroner Annie Groves. "It's just terrible."
Rescuers on the scene since 2 a.m. reported seeing children wandering the area looking for their parents and parents searching for missing children. Children's bicycles and other toys were strewn amid the debris of aluminum siding, mattresses, chairs and insulation.
Five other people were confirmed dead in neighboring Warrick County, east of Evansville, where the Ohio River city of Newburgh was hit. No deaths were immediately reported in Kentucky.
The storm reduced homes to splinters and scattered debris across the countryside. Entire blocks of buildings were nothing but rubble.
Indiana homeland security spokeswoman Pam Bright said about 100 of the 350 or so homes in at the Evansville mobile home park were destroyed and 125 others were damaged.
Larry and Christie Brown rode out the storm inside their mobile home.
"Man, it was more than words can say," Larry Brown said. "We opened the door and there wasn't anything sitting there."
Chad Bennett, assistant fire chief in Newburgh, told CNN that sirens sounded, but most people didn't hear them because it happened in the middle of the night.