Columbia, South Carolina - A jolt of freezing rain and ice across Georgia and the Carolinas early Thursday closed schools, snarled traffic and caused power outages to more than 350,000 customers.

The outages were caused by ice that formed on tree limbs, which then fell onto power lines. About 160,000 were without power in northern South Carolina, 102,000 in northeast Georgia, 57,000 in the Atlanta area and 40,000 in western and central North Carolina.

"The trees and power lines are down everywhere on the road. It's just dangerous to be out," said Rebecca Neal, who was using blankets to keep warm in her powerless Greenville, S.C., home and thinking about finding a hotel for the night.

Earlier in the day, Neal had gone to her job at a public relations firm, only to find that her office didn't have power either.

School systems cancelled or cut short classes from northern Georgia to western stretches of Virginia.

The National Weather Service said the freezing rain was expected to continue in the region through Thursday evening, and overnight temperatures were forecast to dip to about -6 C. More power lines and tree limbs could snap under ice layers expected to grow to up to three-quarters of an inch thick.

Mountains of North Carolina and Virginia were being hit with a hazardous mix of snow and sleet, with accumulations from 2.5 to 7.5 centimetres expected overnight.

"Snow we can plow. Ice we can't," said Virginia Department of Transportation spokesman Chuck Lionberger.

The wintry mix was blamed for a school bus accident in Cherokee County, on the northern end of suburban Atlanta. The driver swerved to avoid a large tree branch that had fallen across the road, forcing the vehicle's rear tires to slide off the road. None of the 23 students aboard the bus was injured.

A spokeswoman for Duke Power, the main supplier of electricity in the hard-hit stretches of the Carolinas, said crews were working to restore power, but added that it could be a long process.