Three additional deaths were reported in Marianna, in Jackson County, Florida, Sheriff Lou Roberts told a news conference on Friday (local time).
The number of fatalities was expected to rise further as no deaths have been reported from oceanfront communities, such as Mexico Beach, Port St. Joe and Panama City, which bore the brunt of the storm's wrath.
"Rescuers have so far been unable to conduct thorough searches there.
"I think you're going to see it climb," Brock Long, administrator of the Federal Emergency Management Agency (FEMA), said of the death count. "We still haven't gotten into some of the hardest-hit areas."
FEMA crews have been using bulldozers and other heavy equipment to push a path through debris to allow rescuers to probe the rubble with sniffer dogs as drone aircraft and Blackhawk helicopters searched from above.