(Reuters) - A massive winter storm rolled eastward to the mid-Atlantic United States on Sunday after dropping more than a foot of snow on parts of the Midwest and killing at least 7 people in highway accidents on Saturday.

The weather system, which started as rain from Mexico but has since turned into snow, is forecast to affect an 1,800-mile (2,900 km) swath of the United States from Colorado to the mid-Atlantic. Millions of Americans in ten states and Washington, D.C. were under a winter storm warning or advisory on Sunday.

Four people in Missouri and three in Kansas died in roadway accidents, authorities in both states reported.

Virginia Governor Ralph Northam declared a state of emergency on Saturday in anticipation of snow and ice accumulation, transportation problems and power outages in the state. Central and northern Virginia may receive up to ten inches of snow, according to the National Weather Service.

Washington was forecast to receive almost a half foot of snow, forcing airlines to cancel over one hundred flights leaving Reagan National Airport on Sunday morning.

(Reporting by Gabriella Borter in New York; Editing by Jeffrey Benkoe)

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