The second wintry storm in two weeks to hit the normally balmy south US has encrusted highways, trees and power lines in ice , knocking out electricity to nearly a half-million homes and businesses.
At least nine traffic deaths across the region were blamed on the treacherous weather, including three people who were killed when an ambulance careened off an icy West Texas road and caught fire.
Nearly 3,300 airline flights nationwide were also canceled.
Forecasters warned of a potentially "catastrophic" storm across the south with more than an 2.5 cms of ice possible in places.
As he did for parts of Georgia, US President Barack Obama declared a disaster in South Carolina, opening the way for federal aid. In Myrtle Beach, South Carolina, palm trees were covered with a thick crust of ice.
As residents across the south heeded forecasters' unusually dire warnings and hunkered down at home against the onslaught of snow and freezing rain, the storm pushed northward, threatening to bring more than 30 cms of snow Thursday (local time) to the already sick-of-winter mid-Atlantic and Northeast.
Ice combined with wind gusts up to 48 kph snapped tree limbs and power lines. More than 200,000 homes and businesses lost electricity in Georgia, 130,000 in South Carolina and nearly 30,000 in Louisiana. Some people could be in the dark for days.
For the mid-Atlantic and the northeast, the heavy weather was the latest in an unending drumbeat of storms that have depleted cities' salt supplies and caused school systems to run out of snow days.
Washington DC could get up to 20 cms of snow, while New York City could see 15 cms.
In an warning issued overnight, National Weather Service called the storm "catastrophic ... crippling ... paralyzing ... choose your adjective."