Millions of Americans were hit by a severe winter storm on Monday that brought heavy snow, ice, strong winds and freezing temperatures as it moved east from the center of the country into the Mid-Atlantic region.

The US National Weather Service issued winter storm watches and warnings stretching from Kansas and Missouri to New Jersey as moderate to heavy snowfall is expected from the Ohio Valley to the Mid-Atlantic region.

A state of emergency was declared Monday morning in at least seven states, including Kansas, Missouri, Kentucky, Virginia, West Virginia, Arkansas and parts of New Jersey. Officials are urging people to stay home and stay off the streets.

According to the National Weather Service, the storm is expected to produce between 6 and 12 inches of snow across the Mid-Atlantic region, including the Washington DC metropolitan area.

The storm hit the US Midwest over the weekend, bringing heavy snow and ice to roads in areas such as Kansas and Missouri.

Kansas City International Airport recorded 11 inches (27 cm) of snow on Sunday, according to the National Weather Service there. This is the fourth-largest single-day snowfall total in Kansas City since records began in 1888.

In Topeka, Kansas, the weather service reported 14.1 inches (36.8 cm) of snow, marking the third-highest single-day snowfall on record for that area.

As of Sunday evening, the Missouri State Highway Patrol reported 1,043 stranded motorists, 356 accidents, 31 injuries and one fatality related to the storm.

Additionally, Missouri State Police reported that another person was killed after being struck by a dump truck that skidded on a slippery road in Jackson County.

The Weather Channel also reported that two people were killed in a car accident in Sedgwick County, Kansas, on Sunday evening.

On Monday, the weather service said another 2 to 4 inches of snow is expected in parts of the Ohio Valley and central Appalachia, where travel disruptions will continue.

As the storm moves toward the Mid-Atlantic region, up to an inch of snow per hour is forecast for Washington Monday morning, with travel conditions expected to worsen.

As of 9 a.m. ET Monday, more than 300,000 customers were experiencing power outages in Kentucky, Indiana, Virginia, West Virginia, Illinois and Missouri, according to PowerOutage.us.

In addition, more than 1,500 flights in the United States were canceled, according to FlightAware.com. Ronald Reagan Washington National Airport has reported the most cancellations so far, with 239 canceled flights as of 10 a.m. ET.

Schools and government offices were closed Monday in several affected areas, including parts of Washington, Virginia, Indiana, Kentucky, Maryland, Pennsylvania and others.

All federal offices in the Washington metropolitan area were also closed on Monday.

And even southern states like Texas, Louisiana and Florida expected wind chills and below-freezing temperatures in some areas on Monday. The National Weather Service has issued freeze warnings for parts of Florida, Georgia, Louisiana and Texas.

The freezing weather is attributed to disruptions in the polar vortex, a large, three-dimensional ring of strong winds. Normally the polar vortex revolves around the North Pole, but occasionally it extends into the United States, Europe or Asia.

So far this winter in the Northern Hemisphere, the polar vortex has contributed to temperatures as low as -55°C (-67°F) in Siberia. And currently the most violent part of the vortex has moved to North America.

According to the Associated Press, studies show that a rapidly warming Arctic is partly responsible for the increasing frequency of the polar vortex, which is expanding its reach.