A blizzard battered the Mid-Atlantic region of the United States on Saturday, quickly dumping large amounts of snow that piled up on roadways and toppled trees onto apartment buildings and cars.

Officials urged people to huddle at home for the weekend, out of the way of crews trying to keep up with a storm that forecasters said could be the biggest for Washington, D.C., in modern history. A father and son were killed in Virginia when a tractor-trailer struck and killed them after they stopped to help another driver.

A record 2 1/2 feet 2.5 feet (75 centimeters) or more was predicted for Washington. As of early Saturday, parts of Maryland had seen up to 20 inches (50 centimeters) of snow and more than 8 inches (20 centimeters) had fallen in D.C. Forecasters expected snowfall rates to only increase, up to 2 inches (5 centimeters) per hour until daybreak.

Blizzard warnings were issued for the District of Columbia, parts of New Jersey and Delaware and some areas west of the Chesapeake Bay.

“Things are fairly manageable, but trees are starting to come down,” said D.C. fire department spokesman Pete Piringer, whose agency responded to some of the falling trees. No injuries were reported.

Airlines cancelled flights, churches called off weekend services and people wondered if they would be stuck at home for several days in a region ill-equipped to deal with so much snow.

Becky Shipp was power-walking in Arlington, Virginia, on Friday.

“D.C. traditionally panics when it comes to snow. This time, it may be more justifiable than most times,” Ms. Shipp said. “I am trying to get a walk in before I am stuck with just the exercise machine in my condo.”

A hospital fire in D.C., started when a snow plow truck caught fire, sent about three dozen patients scurrying from their rooms to safety in a basement.

Authorities blamed the storm for hundreds of accidents. Some area hospitals asked people with four-wheel-drive vehicles to volunteer to pick up doctors and nurses to take them to work.

Shoppers jammed aisles and emptied stores of milk, bread, shovels, driveway salt and other supplies. Many scrambling for food and supplies were too late.

Metro, the Washington-area transit system, closed all but the underground rail service and suspended buses in area that heavily relies on both.

Across the region, transportation officials deployed thousands of trucks and crews and had hundreds of thousands of tons of salt at the ready. Several states exhausted or expected to exhaust their snow removal budgets.

The snow comes less than two months after a Dec. 19 storm dumped more than 16 inches (40 centimeters) on Washington. Snowfalls of this magnitude {mdash} let alone two in one season {mdash} are rare in the area. According to the National Weather Service, Washington has received more than a foot (30 centimeters) of snow only 13 times since 1870.

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