ATLANTA (REUTERS) - A deadly winter storm potentially more destructive than the one that paralysed Atlanta just two weeks ago gripped the southern United States (US) on Wednesday, crippling travel, knocking out power to more than 330,000 customers and encasing magnolia trees and palmetto fronds in ice.

The weather was blamed for at least 10 deaths throughout the region, including three who were killed when an ambulance transporting a patient skidded off an icy road in Carlsbad, Texas, about 386km south-west of Dallas, the Texas Department of Public Safety said on Wednesday.

Road conditions quickly deteriorated in South Carolina and North Carolina on Wednesday afternoon, creating a nightmarish commute for drivers in a hurry to get home as the snowfall got heavier and the ice thickened.

Mr Sam Bellezza, a high school teacher who lives in Raleigh, was headed to Home Depot for supplies. It started snowing while he was there and the drive home, which normally takes 10 minutes, took more than two hours, he said.

Some people left their cars behind and were walking along the snowy banks, Mr Bellezza said.

"All these cars were wrecking and falling into a ditch," he said. "It was all bumper cars and people yelling and screaming at one another."

Fatal road accidents also were reported in Mississippi and South Carolina.

More than 3,300 US flights were cancelled and about 2,000 delayed on Wednesday, according to flight-tracking website FlightAware.com. Hardest hit were Hartsfield-Jackson International Airport in Atlanta and Charlotte Douglas International Airport in North Carolina.

As the storm moved north, some public transportation in Washington, DC, including service for disabled riders, was cancelled by mid-afternoon on Wednesday. Philadelphia announced that public and parochial schools, as well as all state courts, would be closed on Thursday.

Hundreds of schools across the South, perhaps heeding lessons learned in the last storm, which trapped 11,000 students overnight in Alabama, announced they would be closed on Wednesday and Thursday.

In Georgia, state employees on Tuesday made a trip to the Georgia Academy for the Blind in Macon, about 133km south-east of Atlanta, to pick up four students who had no way to get home, said Governor Nathan Deal.

GEORGIA ROADS EMPTY

Most motorists in Georgia, where thousands were stranded in their vehicles during the last weather front, stayed off the roads after a state of emergency was declared, Mr Deal said.

Vehicles that did venture out were soon coated with ice, their radio antennas looking like skewers of ice cubes, television images showed.

A possibly historic accumulation of ice as well as heavy snow was expected to add up to nearly 20.3cm of white stuff for Charlotte, and 23cm forecast for Spartanburg, South Carolina, meteorologists said.

The worsening storm stretched from Mississippi to the Carolinas, and was likely to intensify on Wednesday evening as it moved up the East Coast into the northern states, the National Weather Service said.

More than an inch of ice was possible from central Georgia into South Carolina by Thursday morning, according to forecasters.

"Oh, Lord. It's pretty slick out there," said Mr Fred Neely, 69, a retiree living in Florence, South Carolina.

Heavy ice and snow toppled trees onto power lines, cutting off electricity to more than 334,000 customers shivering in a region accustomed to mild winters. More than a third of them were in Georgia, where some residents may have to wait up to a week for power to be restored, said Georgia Power spokesman Amy Fink.

"It does appear that the storm could have an even greater impact than we originally had predicted," Ms Fink said.

Shelters were opened in Georgia, Alabama and North Carolina to help those stranded by the storm.

The brutal weather was some of the worst seen in the region in a decade or more.

The last significant ice storm in Georgia was in January 2000, when up to half 1.3cm of ice left more than 350,000 people without power, weather service meteorologist Dan Darbe said.

With the latest storm, "we're talking a much larger area and a much larger amount of ice", he said.