The second wintry storm in two weeks to hit the normally warm US South has encased the region in ice, knocking out electricity to hundreds of thousands of homes and businesses before pushing toward the heavily populated Northeast.

At least 11 deaths across the region were blamed on the treacherous weather on Wednesday. Nearly 3,300 flights were cancelled.

US President Barack Obama declared a disaster in South Carolina and for parts of Georgia, opening the way for federal aid. In Myrtle Beach, South Carolina, palm trees were covered with a thick crust of ice.

The storm has moved northward, threatening to bring more than a foot (30 centimetres) of snow today to the mid-Atlantic and Northeast.