The tornado, the deadliest to hit Indiana since 1974, struck a horse racing track near Henderson, Ky., then crossed into Indiana, triggering emergency sirens that many people, fast asleep, did not hear.
Stephanie Segretto of CBS affiliate WLKY-TV reports it hit around 2:30 in the morning.
At least 17 people, including three children, died at a mobile home park in Vanderburgh County and five others died in neighboring Warrick County, east of Evansville. More than 100 people were taken to hospitals.
"They were in trailer homes, homes that were just torn apart by the storm," Deputy Vanderburgh County Coroner Annie Groves said. "It's just terrible."
"It exploded, it just exploded, and other people's trailers were inside of ours," Stacy Wright told CBS News. "We found kids inside our trailer buried under our stuff."
Rescuers continued searching Eastbrook Mobile Home Park throughout the night. They roamed what had been yards or basements, holding flashlights and lifting debris to make sure no one was underneath.
Cranes lifted toppled mobile homes, and forklifts moved smashed cars into organized rows. Other heavy equipment rumbled through the debris as night fell and the air became crisp and cool.
All the dead were in Indiana. The youngest victim was a 2-year-old boy who was killed along with his 61-year-old grandmother, the coroner's office said.
Gov. Mitch Daniels, describing the destruction as random and brutal, nearly broke down.
"They lost a whole family of four, including a pregnant mom," Daniels said haltingly.
Marsha Tweedy broke into tears Sunday as she walked through the remains of the Warrick County farmhouse where her 28-year-old daughter, Cheryl Warren, died.
The storm killed Warren — a dental assistant who was eight months pregnant — her 4-year-old son, Isaac, and her husband, Jeremy, a truck driver.
"They were a beautiful family," Tweedy said. "They didn't have much, but they enjoyed everything they had."
A loud roar was all the warning many residents got, reports CBS News correspondent Cynthia Bowers. Most were sound asleep when the sirens sounded early Sunday and, in truth, there likely was no place to hide from the fiercest tornado to hit Indiana in more than 30 years.
Tim Martin, 42, said he and his parents were awakened by the wind, which lifted their mobile home and moved it halfway into the neighbor's yard.
They escaped unharmed, but he said they heard several neighbors calling for help. A neighboring mobile home was overturned, he said, and another appeared to have been destroyed.