More heavy snow is forecast to add to the chaos brought to the east coast of the United States by a vicious winter storm.

A further six to 15 inches (15 to 38cm) is expected to hit the region over the next few hours.

Thousands of people have already been left shivering, stranded in their cars or waiting at airports after earlier heavy snow blanketed the coast from South Carolina to Maine.

States of emergency were declared in parts of Georgia, North Carolina and Maryland, with the National Guard called in to help clear roads and rescue motorists.

At least four people have died from exposure or weather-related traffic accidents in the Carolinas.

Meteorologists were taken by surprise by the ferocity of the original storm which raced north along the coast on Monday and Tuesday.

Power cuts

Weather forecasting computers had said the mainland would be spared the worst of the storm and had predicted only one inch of snow.

But in some places nearly two feet fell.

Andrew Woodcock, a meteorologist with the National Weather Service in Sterling, Virginia, said: "We're really cursing those computer models.

"They had the low [pressure system] way out to sea."

The blizzard has caused delays and temporary shutdowns at major airports, and left many schools and businesses closed for a third day.

Tens of thousands of homes are also still without power.

Stranded

Hundreds of motorists waited for help on Wednesday along Interstate 85 in North Carolina, which was virtually shut down for a 20-mile (32-kilometre) stretch near the Virginia state line.

National Guardsmen and Highway Patrol officers were sent to help.

Some of the stranded motorists had been in their cars since Tuesday afternoon, they told media outlets by cellular phone.

Georgia is also reeling from a weekend ice storm that caused an estimated $35 million in damage.