More than 729,000 customers were without power in the Southeast, power companies told CNN. More than 210,000 were Georgia Power customers, the utility said.
South Carolina was the hardest hit, with about 220,000 customers without electricity, while Wilmington, North Carolina, accounted for more than 58,000 outages.
The utilities said Wednesday morning they expect those numbers to rise over the next 24 hours.
Georgia Power, the state's largest utility, warned that hundreds of thousands could be without electricity for days.
"This has the opportunity to be a huge event when you're talking about the amount of ice you're looking at," Aaron Strickland, Georgia Power's emergency operations chief, told reporters.
The utility staged fleets of trucks across the area. Teams from Florida, Texas and Ohio bolstered local line crews.