Watch: Snow blankets parts of New York and Nebraska
A huge winter storm has brought snow, ice and and freezing temperatures to a broad swathe of the US, with more than 60 million Americans under weather alerts.
Forecasters say the extreme weather - named Storm Blair - is being caused by the polar vortex, an area of cold air that circulates around the Arctic.
A state of emergency has been declared in seven US states, with much of Canada also under weather alerts, as the blizzard conditions have dumped about a foot of snow (30cm) in places.
Thousands of flights have been cancelled or delayed, as forecasters say the winter storm could bring the heaviest snowfall and coldest temperatures in more than a decade.
Watch: Heavy snow as severe US winter storm moves east
Thirty US states, spanning from the middle of the country to the east coast - including major cities such as Washington DC and Philadelphia - are under weather alerts, the National Weather Service (NWS) said.
A state of emergency has been declared in the states of Kansas, Missouri, Kentucky, Virginia, West Virginia, Arkansas and parts of New Jersey.
Sunday was forecast to be the most intense day of the storm for many of the affected states, cutting off roads, shutting down schools and forcing the cancellation of thousands of flights.
Blizzard warnings have been issued in Kansas, Missouri and Nebraska.
Kansas City is seeing its heaviest snow in 32 years, with more than a foot (30 to 40cm) having come down so far, according to Matthew Cappucci, a senior meteorologist at the weather app MyRadar.
Parts of northern Missouri have already experienced 14in (36cm) of sleet and snow.
The storm has begun easing as it moves towards the US's east coast, with parts of Virginia, Maryland, Washington DC and Delaware due to take the brunt of the weather on Monday.
Washington DC was bracing for heavy snow and bitter cold on Monday, the same day the US Congress is set to meet and formally certify Republican Donald Trump's election as president.
Republican House Speaker Mike Johnson said the weather would not prevent lawmakers from carrying out their duties. But officials have announced that federal offices in the nation's capital will be closed.
Getty ImagesA cargo jet parked in the snow at Louisville airport on Sunday
The NWS said the winter storm could bring "the heaviest snowfall in at least a decade", while AccuWeather forecaster Dan DePodwin said: "This could lead to the coldest January for the US since 2011."
He added that "temperatures that are well below historical average" could linger for a week. Temperatures 12-25F (7-14C) below normal are forecast.
More than 1,700 flights into and out of the US were cancelled on Sunday and about 8,300 more were delayed, according to FlightAware.com.
Getty ImagesKentucky firefighters shovel snow
Amtrak has also cancelled numerous train services.
American, Delta, Southwest and United airlines are waiving change fees for passengers because of the potential flight disruptions.
Further north, Canadians are also feeling the effects of the polar vortex.
Much of Canada has been under extreme weather alerts, with freezing temperatures spanning the country.
Some areas are also seeing snow squalls - a sudden heavy snowfall accompanied by strong winds.
In the central province of Manitoba, the wind chill could see temperatures plummet to as low as -40C.
Meanwhile, as much as 15in (38cm) of snow was expected in parts of Ontario on Sunday.
Getty ImagesA deserted highway in Shawnee, Kansas, on Sunday
Conditions on roads have deteriorated, with crashes involving lorries and cars, as well as a fire engine rolling over near Salina, Kansas.
"Whiteout conditions will make travel extremely hazardous, with impassable roads and a high risk of motorists becoming stranded," the NWS warned.
Meanwhile, severe thunderstorms capable of producing tornadoes were set to move east from Arkansas and Louisiana into Mississippi and Alabama on Sunday evening, the NWS said.
Private meteorologist Ryan Maue said: "It's going to be a mess, a potential disaster. This is something we haven't seen in quite a while."
