WASHINGTON - A blizzard-like storm rocked the Mid-Atlantic and Northeast yesterday, crippling travel across the region and leaving hundreds of thousands of customers without power.

Five deaths appeared to have been caused by the storm system, which stretched from the Carolinas north to New England and also spread into some Midwestern states. The 14 inches of snow that fell at Reagan National Airport outside Washington was the most ever recorded for a single December day.

The National Guard used humvees to rescue stranded motorists in Virginia, and about 500 people had sought warmth and refuge in emergency shelters.

"The snow has not stopped falling, the storm isn't over, and folks should not think this is crying wolf," said Laura Southard, a spokeswoman for the Virginia Department of Emergency Management.

More than two feet of snow fell in some areas since Friday, and the nation's capital was under a blizzard warning. Public transportation nearly ground to a halt.

The slow-moving storm was headed to the Northeast, where forecasters said parts of Connecticut, Rhode Island, and Massachusetts could see more than 16 inches by tonight. Forecasters expected the storm to drop as much as 10 inches on New York.

Snowplows cleared the runway at Andrews Air Force Base in suburban Washington as President Obama returned from climate talks in Copenhagen. The White House said that, because of the conditions, Obama rode in a motorcade back to the White House, instead of taking his helicopter.

The region was virtually a sea of white. The Smithsonian Institution closed its museums, and the National Mall, which normally would be swarming with tourists, instead was the scene of snowball fights and cross-country skiers.

In western Virginia, officials said several hundred motorists became stranded and had to be rescued by four-wheel-drive vehicles.

"Some folks have decided to stay in vehicles, others have been taken to shelters," said Virginia Department of Emergency Management spokesman Bob Spieldenner. "We're definitely trying to keep people off the roads. Troopers had responded to more than 4,000 traffic crashes and disabled vehicles."

One person in Virginia was killed in a traffic accident caused by slick roads, and authorities said the weather may have contributed to another traffic death. A third death is believed to have been caused by exposure. In Ohio, two people were killed in accidents on snow-covered roads hit by the same storm system.

Mayors in Washington and Philadelphia declared snow emergencies, and forecasters said the conditions could worsen. Governors in Virginia, West Virginia, Kentucky, and Delaware declared states of emergency.

Most of the flights at Reagan National and Dulles International Airport had been canceled, creating a ripple effect of delays across the country. The runways at Reagan were closed until 6 a.m. today. Dulles had one runway open, but was expecting few, if any, flights. Baltimore-Washington International Thurgood Marshall Airport closed temporarily yesterday afternoon to allow crews to clear snow from the runways.

Travelers who tried to reach their destinations by train also faced long delays and threats of cancellations.

Washington's Union Station was full of travelers, some of them sprawled on the floor. Amtrak said delays between Washington and Boston were averaging 30 to 60 minutes. However, at least two trains to Boston departed more than four hours late, according to the railroad's Web site.