Emergency responders searched into the night for more victims in Lone Grove, where all of the victims died Tuesday and 14 people were seriously injured, said Oklahoma Department of Emergency Management spokeswoman Michelann Ooten.
She said the National Guard was being sent to help local authorities.
"We will do everything we can to get Oklahomans the assistance they need," Gov. Brad Henry said.
Buildings were damaged or destroyed throughout the town of about 4,600, some 100 miles south of Oklahoma City, said Chester Agan, assistant emergency manager for Carter County.
However, much of the most severe damage appeared to be centered in two mobile home parks that were "pretty much wiped out," said Dave Smith, a paramedic who helped in the first emergency response.
The eight confirmed deaths included seven people in Lone Grove and a truck driver who was driving through the area, said Robert Deaton, interim chief investigator for state Medical Examiner's office.