Emergency teams in Georgia, Mississippi and Alabama were working to assess the damage as the storm moved towards North and South Carolina and southern Virginia, the National Weather Service said.
Alabama Governor Robert Bentley has declared emergency after reports of tornado touchdowns in at least six counties.
Injuries were reported in Sumter and Marengo counties, with at least one fatality in the latter, he said.
Three people were killed in Autauga county after fallen trees crashed into mobile homes in the area, police said.
Three deaths were reported in Washington county, said Yasamie August, spokeswoman for the Alabama Emergency Management Agency. Two deaths were reported in Oklahoma and seven in Arkansas.
In Greene county, one death and six injuries were reported, officials said. Mississippi suffered “extensive damage” when a tornado touched down, according to Mississippi’s Emergency Management Agency. The city mayor said no one was injured in the storm, which tore the roof from a hotel and caused damage to a bank and many homes.