At least 10 people have died and thousands are without power
A massive blizzard which forecasters say could be among the 10 worst to affect the north-eastern United States is hammering the country's capital.
Up to 2ft (60cm) of snow fell on Washington DC and Baltimore this morning, with schools closed, thousands of flights cancelled and a state of emergency declared across a vast area.
This morning, it was snowing heavily in the city, and experts predicted it would continue for hours more.
"I want to be very clear with everybody. We see this as a major storm. It has life and death implications," Washington Mayor Muriel Bowser warned.
In total, some 85 million people in at least 20 states are in the storm's path.
By 7am local time the storm had dumped snow in 14 states, including 18 inches in Kentucky, as it continued to move eastward.
The National Weather Service said seven inches of snow fell in Washington.
Snowfall amounts in nearby Maryland ranged between 4.5 inches in Baltimore and 13.5 inches in Oakland.
Virginia State Police say they responded to nearly 1,000 traffic crashes as the fearsome storm blanketed the state with snow.
Meanwhile, utility companies in New Jersey reported that nearly 40,000 customers are without power, the majority along the coast.
Flight tracking site FlightAware estimates more than 1,100 flights originally scheduled for Friday and Saturday within, into or out of the United States have been cancelled so far.
An additional 7,000 flights were delayed on Friday alone.
Scheduled services from Dublin by United Airlines to Newark, American Airlines to Philadelphia, Aer Lingus to New York and Delta's flight also to New York were among those affected.
All major airlines have issued travel waivers over the weekend, allowing passengers to rebook to avoid the storms.
A bobcat piles up snow in front of the US Capitol. Image: Alex Brandon / AP/Press Association Images
State of emergency
The National Weather Service said the winter storm could rank near the top 10 to ever hit the region.
NWS meteorologist Paul Kocin compared the storm to Snowmageddon, the first of two storms that "wiped out" Washington in 2010 and saw 30 inches of snow.
Louis Uccellini, director of the weather service, said: "It does have the potential to be an extremely dangerous storm."
He said the elements look set to combine to create a blizzard with strong winds, dangerous inland flooding, white-out conditions and the possibility of thunder snow - when lightning strikes through a snowstorm.
The snowfall, which is forecast to continue into Sunday, could cause as much as $1bn in damage.
Up to 18 inches of snow is also predicted for Philadelphia and New York, where Mayor Bill de Blasio has declared an emergency.
Around 1,000 track workers will be deployed to keep New York's subway system moving and 79 trains will be fitted with "scraper shoes" to reduce icing on rails.
A state of emergency has also been declared in New Jersey, Tennessee, North Carolina, Virginia, Maryland, Pennsylvania, the District of Columbia and parts of other states.
Blizzard warnings are in place from Arkansas to as far north as New York.
At least 10 people have died in storm-related crashes in Tennessee, Kentucky and North Carolina, officials said.
Authorities in Tennessee said a woman was killed after her vehicle slid off an icy road and down a 300ft (91m) embankment.
Her husband, who survived the crash, took several hours to climb the embankment and call for help.
Schools and government offices have been closed and the shelves of stores emptied as millions of people stocked up.
Authorities have said the subway system in the capital will shut down entirely on Friday night and remain closed into Sunday for safety reasons.
Underground stations usually stay open during major snowstorms.
White House spokesman Josh Earnest said President Obama will hunker down at the White House.
However, giant panda Tian Tian woke up this morning to a lot of snow, and he was pretty excited about it.