A powerful winter storm churning up the US East Coast has brought snowfall and gusting winds to a wide swath of the country as forecasters issued dire warnings for the millions of people in its path.

The storm has strengthened into a "bomb cyclone," the dramatic name for what happens when a storm's pressure plummets as it explosively strengthens - and this particular storm is among the most explosive ever observed on the East Coast. After first blasting the Southeast with cold and snow, dropping up to 15 centimetres in the Carolinas, the storm hugged the coastline and continued to head north.

The National Weather Service said the year's first winter storm "will continue to rapidly intensify through Thursday night," moving quickly up the East Coast. Even though the heaviest precipitation is expected to remain over the Atlantic Ocean, some of the "significant snow" will impact areas stretching from North Carolina to Maine, the Weather Service said.

The impact will vary depending on location. The nation's capital saw a light dusting, while New York City is forecast to receive as much as 20 centimetres of snow. In parts of New England, the forecasts are more dire, warning of potentially more than 30 centimetres of snow and possible blizzard conditions. Blizzard warnings stretched from Connecticut to New Hampshire.