WASHINGTON (AFP) - A monster blizzard threatening the US East Coast hit Washington on Friday, as officials warned the millions of people in the storm's path to take shelter from potentially deadly snowfall and biting wind gusts.
Over the next 36 hours, forecasters predict the storm will dump 61cm of snow in the capital and surrounding areas, bringing life to a wintry halt as residents ride out the storm.
A blizzard warning was in effect for a large swath of the eastern United States from Washington up to New York, the National Weather Service (NWS) said. Several southern states were already hit by snow and sleet.
Thousands of flights were cancelled and grocery store shelves laid bare in preparation for the storm, which was dubbed "Snowzilla" by The Washington Post's weather team.
Before the snow started to fall on Washington in the early afternoon, Mayor Muriel Bowser urged residents to go home and stay there.
"I want to be very clear with everybody. We see this as a major storm. It has life and death implications," Bowser told reporters.
Schools and government offices were all closed, with public transport scheduled to shut down in the evening until early Monday.
"Visibility will be reduced to near zero at times in whiteout conditions," NWS reported in its bulletin for Washington.
"Heavy snow and blowing snow will cause dangerous conditions and will be a threat to life and property. Travel is expected to be severely limited if not impossible during the height of the storm," it added.
NWS director Louis Uccellini said Thursday the system had the potential to "affect over 50 million people."
So far, more than 6,200 flights originally scheduled for Friday and Saturday within, into or out of the United States have been cancelled, according to the flight monitor flightaware.com.
With authorities warning the storm could bury Washington under more snow than it has seen in nearly a century, officials took the unusual step of closing down the city's rail and bus system from Friday night until Monday morning.
The Metro system - the second busiest in the United States after New York - serves about 700,000 customers a day in Washington, Maryland and Virginia.
It was likely to be the longest closing in the system's 40-plus year history, The Washington Post reported.
Grocery store shelves were bare - with toilet paper, milk, bread and alcohol conspicuously missing - as residents anticipated impassable roads and power outages.
"I think it's going to be a disaster," Sharonda Brown, a nurse, said as she waited for an Uber car in Washington with a full cart of groceries.
If the blizzard leaves as much snow in Washington as forecast, it could surpass a record set in 1922 by a storm that dumped over 70cm over three days and killed 100 people after a roof collapsed at a theatre.
US Capitol Police have said they were lifting a decades-old sledding ban, but the National Monuments, US Capitol building and Smithsonian museums would all be closed.
Even a massive snowball fight in Washington's Dupont Circle neighbourhood, which nearly two thousand people said they would attend on Facebook, had to be postponed from Saturday to Sunday due to the storm's ferocity.
Snow and sleet has already hit the southern states of Arkansas, Tennessee, Kentucky, North Carolina, West Virginia and Virginia, with 18 states under blizzard or other winter storm warnings, the Weather Channel reported.
"People are staying home and that is extremely important for our citizens. We're having a lot of accidents," North Carolina Governor Pat McCrory told CNN.
Nearly 20,000 people were without power in the state, emergency officials said on Twitter.
Meanwhile, footage showed cars slipping and sliding in the southern city of Nashville, as middle Tennessee faced its biggest snowstorm in 13 years, The Tennessean reported.
Further north, in New York, the storm is expected to dump up to 30cm from early Saturday to midday Sunday, NWS reported.
"Any unnecessary driving should be avoided. Unless urgent, stay off the roads," Mayor Bill de Blasio told a news conference.
"Do not bring out your vehicle tomorrow and any vehicle blocking a roadway tomorrow will be towed."
The city will enforce a local winter weather emergency and is braced for potential flooding in coastal areas, he said.
The frigid weather marks a stark departure from what has otherwise been a mild winter along the eastern seaboard.
Just a month ago on Christmas Eve, the NWS reported that temperatures in New York's Central Park peaked at 22 deg C, the warmest ever for the day since records began in 1871.