WASHINGTON » A snowstorm 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 16 inches of snow that fell at Reagan National Airport outside Washington was the most ever recorded for a single December day, while about 16 inches had also fallen in Philadelphia.

Those who did venture out were treated to nearly desolate stores on what is usually one of the busiest shopping days of the year. There were virtually no lines to get a picture with a mall Santa on the last weekend before Christmas.

The National Guard used Humvees to rescue stranded motorists in Virginia and some 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 has fallen in some areas since Friday. Thirty inches of snow was reported in Wintergreen, Va., at the foot of the Blue Ridge Mountains outside Charlottesville. In the nation's capital, 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 many as 10 inches on New York City.

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

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.

For Chris and Kelly Fitzpatrick, who were visiting from Clearwater, Fla., the winter wonderland came at the perfect time.

“;It's her fault that we're out so long. She wants to walk and walk and walk,”; said Chris Fitzpatrick, 38.

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

Virginia State Police spokeswoman Corinne Geller said traffic was moving, though slowly. There were reports of jackknifed tractor-trailers and some semis on their sides. 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.

At Crump's Store at the intersection of two country roads outside Richmond, Va., owner Suzanne Rudd stood with a man dressed as Santa and waved to the few motorists who dared to hit the slick roads. Rudd said only a few children had come to visit with Santa.

“;Normally we'd have a long line here but people are having a hard time getting out,”; Rudd said.

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.

“;It's going to be an all-day thing. It's going to be on and off,”; said National Weather Service meteorologist Kevin Witt in Sterling, Va.

Most flights were canceled at Reagan National Airport and Dulles International Airport near Washington, Philadelphia International Airport and at Newark Liberty International Airport in New Jersey, creating a ripple effect of delays across the country. BWI Thurgood Marshall Airport near Baltimore also closed yesterday afternoon, and travelers who tried to reach their destinations by train also faced long delays and threats of cancellations.

“;It's going to be very challenging for people who weren't able to get out today to rebook on flights this week,”; said Tara Hamilton, a spokeswoman for the Metropolitan Washington Airports Authority.

Washington's Union Station was full of travelers, some of them sprawled on the floor. Other travelers were stuck on the tracks. A train with 255 passengers was stopped in northern Virginia for around six hours yesterday because of a frozen track switch, said Amtrak spokeswoman Vernae Graham. The train arrived at a station in Alexandria at 9:11 p.m.

Delays were also reported for trains between Washington and Boston.

Forecasters said the storm system was expected to generate winds up to 35 miles per hour, which could cause near-whiteout conditions.

At a Walmart in the Richmond, Va., area, Nnika White took advantage of the few shoppers, buying a drum set for her 2 1/2 year old son. White, dressed in heavy winter clothing, said she works long hours at the law firm she owns and doesn't get much time to shop.

“;It's nice because no one's here. For shopping, it's great, but the roads are very, very bad,”; she said.

The storm came from the Gulf of Mexico and drenched South Florida with rain starting late Thursday, leaving flooded homes and stranded drivers.