The latest winter storm to hit the East Coast of the US has grounded more than 6,500 flights, while hundreds of thousands in the ice-encrusted south remained without power.
In the capital, Washington had at least 20cm of snow, and federal offices and the city's two main airports were closed on Thursday. New York City reported a similar amount of snow.
At least 20 deaths, most of them in traffic accidents, were blamed on the storm as it made its way across the south and up the coast, the AP news agency reported.
Among the victims was a pregnant woman who was struck and killed by a snowplough in New York City. Her baby was delivered in critical condition via caesarean section.
"Snow has become a four-letter word," said Tom McGarrigle, chairman of the Delaware County Council in suburban Philadelphia.
The White House cancelled its daily news briefing, and federal agencies told workers to stay home.
The Federal Emergency Management Agency (FEMA) said it had contacted state emergency offices in densely populated Maryland, Pennsylvania and Virginia to assess their assistance needs, the AFP news agency reported.
In addition to the FEMA aid, various localities across the region had readied emergency shelters at churches and recreation centres where residents could stay warm should they lose power.
Military personnel had also been mobilised, with more than 2,300 Army and Air National Guard pressed into action, according to a Pentagon statement.
In New York City, the teachers union blasted Mayor Bill de Blasio's decision to keep the schools open.
Television personality Al Roker, who was in Russia for the Winter Olympics but has a daughter in a New York public school, said on Twitter: "It's going to take some kid or kids getting hurt before this goofball policy gets changed."
The mayor said many parents depend on schools to watch over their children while they are at work.
About 750,000 homes and businesses were left without power in Georgia, South Carolina, North Carolina and Alabama, with scattered outages reported in the mid-Atlantic.
More than 200,000 households and businesses in the Atlanta area alone were waiting for the electricity to come back on.
Temperatures were expected to drop below freezing again overnight, AP reported.
The recent series of storms and cold blasts, blamed in part on a kink in the jet stream, the high-altitude air currents that dictate weather, has cut into retail sales across the US, the Commerce Department said.
Sales dipped to 0.4 percent in January.
"It's been a tough winter. It seems like it will never end," said Deb Ragan, clearing a pavement in Philadelphia.
The dangerous weather also threatened to disrupt deliveries of Valentine's Day flowers.
"It's a godawful thing," said Mike Flood, owner of Falls Church Florist in Virginia. "We're going to lose money, there's no doubt about it."