A massive winter storm barrelling toward Washington DC is poised to drop near-record snowfalls on the US capital before walloping New York and other east coast cities.
The National Weather Service described the system as "potentially crippling" for a swath of the country's northeast, with snowfall exceeding 60cm in Baltimore and Washington DC.
A blizzard watch was issued for New York City and parts of Long Island and New Jersey for early Saturday.
Snow accumulation could reach 30cm in the region, forecasters said.
Southeastern Pennsylvania, including Philadelphia, was expecting 25 to 42cm of snow.
To the south, significant icing was likely for portions of Kentucky and North Carolina, the National Weather Service said.
Millions of residents in the storm's path scrambled to prepare for the weekend weather event, picking stores clean of bottled water, food and other supplies.
Federal employees in the Washington area were told their offices would close at noon on Friday to allow them to get home safely before the snow begins piling up in the afternoon. Public schools were closed.
The Washington Metropolitan Area Transit Authority, which includes the second-busiest US subway system, took the rare step of suspending operations from late Friday through Sunday.
The Virginia National Guard said it planned to bring in up to 300 troops to assist in response operations.
Airlines have also cancelled Friday and Saturday flights, with many of the 2200 cancellations for Friday, most of them at airports in North Carolina and Washington, according to FlightAware.com.
Washington Mayor Muriel Bowser and New York Mayor Bill de Blasio urged motorists to stay off roads starting on Friday amid icy and whiteout conditions.
The storm also forced many to amend weekend activities, with Washington residents planning mass sledding events and a large snowball fight on Sunday.
New York cancelled its Winter Jam in Central Park, a winter sports festival set for Saturday, in anticipation of the storm's arrival.
AccuWeather Senior Meteorologist Alex Sosnowski said the storm taking aim at Washington could rank among the biggest snowfalls on record, eclipsing the "Snowmageddon" storm of 2010 that dropped 45.2cm.
The largest snowstorm in recorded history in Washington was the 1922 Knickerbocker storm, which buried the city under 71 cm.
