A winter blast of snow, ice, wind and plunging temperatures in the United States has created dangerous travel conditions from the central and southern states to the east coast.
The extreme conditions prompted schools and government offices in several states to close early on Monday, local time.
Snow and ice blanketed major roads across Kansas, western Nebraska and parts of Indiana, where the state's National Guard was activated to help stranded motorists.
At least 20 centimetres of snow was expected, along with gusting winds up to 72 kilometres per hour.
The National Weather Service issued winter storm warnings from Kansas and Missouri to New Jersey.
"For locations in this region that receive the highest snow totals, it may be the heaviest snowfall in at least a decade," the weather service said.
The polar vortex of ultra-cold air usually spins around the North Pole.
People in the US, Europe and Asia experience its intense cold when the vortex escapes and plunges southward.
Studies show a fast-warming Arctic is partly to blame for the increasing frequency of the polar vortex extending its icy grip.
Maryland declares state of emergency
School closures were expected to be widespread on Monday, with districts in Indiana, Virginia and Kentucky announcing cancellations and delays on Sunday afternoon.
Classes have also been cancelled in Maryland, where Governor Wes Moore declared a state of emergency on Sunday and announced the state government would be closed on Monday.
"Keeping Marylanders safe is our top priority. Please stay off the roads during this storm. Prepare your home and family and charge your communications devices in case you lose power," Mr Moore said in a statement.
Car wrecks proliferate as storm hits
Over the weekend, at least 600 motorists were stranded in Missouri, authorities said.
Hundreds of car accidents were also reported in Virginia, Indiana, Kansas and Kentucky, where a state trooper was treated for non-life-threatening injuries after his patrol car was hit.
Kentucky Governor Andy Beshear, who also declared a state emergency, said government buildings would be closed Monday.
"We see far too many wrecks out there for people that do not have to be on the roads, so I want to ask: Stay inside," Mr Beshear said.
Virginia State Police reported at least 135 crashes as the storm entered the state on Sunday.
In Charleston, West Virginia, authorities urged motorists to stay home.
Snow and ice forecast
In Indiana, snow covered portions of Interstate 64, Interstate 69 and US Route 41, prompting Indiana State Police to plead with motorists to stay off the roads as ploughs worked to keep up.
"It's snowing so hard, the snowploughs go through and then within a half hour the roadways are completely covered again," Police Sergeant Todd Ringle said.
Roughly 25cm of snow fell in Kansas, with eventual totals predicted to top 36cm for parts of that state and northern Missouri.
In Kentucky, Louisville recorded 19.5cm of snow on Sunday, a new record for the date that shattered the previous mark of 7.6cm set in 1910.
The storm was forecast to move into the Ohio Valley and reach the Mid-Atlantic states on Monday, with a hard freeze expected as far south as Florida. Winds downed trees around the Deep South on Sunday.
The storms also caused havoc for the nation's passenger railways with more than 20 cancellations on Sunday and about 40 planned on Monday.
Nearly 200 flights in and out of St Louis Lambert International Airport were cancelled, according to tracking platform FlightAware.
Temperatures expected to plunge
Starting on Monday, the eastern two-thirds of the US will experience dangerous, bone-chilling cold and wind chills, forecasters said.
Temperatures could be 7 to 14 degrees Celsius below normal.
In Chicago, temperatures on Sunday hovered between minus 7C to 10C and dropped to minus 11.7C in International Falls, Minnesota, on the Canadian border.
The north-eastern states are more likely to experience several days of cold after a mostly mild start to winter, said National Weather Service meteorologist Jon Palmer in Gray, Maine.
The cold air likely will grip the eastern US as far south as Georgia with parts of the east coast experiencing single-digit lows, Mr Palmer said.
AP
