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.
The storm system also was taking its toll on travel.
Amtrak suspended some rail service in the Northeast, South and Mid-Atlantic regions for Wednesday.
Nationwide, more than 3,400 flights were canceled Wednesday and even more than 4,100 were scrubbed for Thursday, according to FlightAware.com.
Among the canceled flights were more than 1,600 in and out of Atlanta's Hartsfield-Jackson Internationanl Airport. Charlotte Douglas International and Raleigh-Durham International airports accounted for the majority of other flights canceled.
At least 10 deaths have been blamed on the weather, including a 55-year-old man who was killed in a head-on collision in Virginia, authorities said. Two people were killed in Georgia, and two died in North Carolina, they said.
In Texas, three people died when an ambulance driver lost control on an icy patch of road outside of Carlsbad, the state Department of Public Safety said. A patient, a paramedic and another passenger were pronounced dead at the scene.
In Mississippi, authorities blamed the storm for two traffic deaths.