Visibility is limited of the Reflecting Pool, seen from the steps of the Lincoln Memorial as snow falls in Washington. (Charlees Dharapak/Associated Press)A winter storm that threatened to dump 75 centimetres of snow on Washington, D.C., sent people flocking to stores Friday to buy shovels and groceries in the U.S. Mid-Atlantic region.

The U.S. National Weather Service warned Friday that the storm could be "extremely dangerous," with heavy, wet snow and high winds expected to make travel difficult as the storm gained strength into Friday night. Snow began falling early Friday afternoon in Washington and was expected to continue falling through Saturday.

Many schools in the city and the surrounding suburbs closed early and the mayor of D.C. declared a snow emergency.

"We are going to be right up against the most snow this city has ever seen," Mayor Adrian Fenty said.

Stores reported empty shelves as people snapped up food and shovels.

"I was looking for salt and shovels and of course they're out," said Colleen Sport, 42, who recently moved to the Washington area from Atlanta.

D.C.'s public transit system cancelled all above-ground services on Friday night and for most of the weekend, while airlines cancelled hundreds of flights in and out of area airports.

The city's transportation department urged motorists to stay off the streets so that work crews could clear roadways. Hundreds of city workers, including contracted employees, began 12-hour shifts on Friday morning, pre-treating roads using about 270 salt trucks.

A traditional D.C. winter doesn't normally result in anything more than a couple of light snowfalls a year, amounting to rarely more than a sprinkling by Canadian standards.

Consequently, the city and its suburbs in Virginia and Maryland don't budget much for snow removal, which means a major snowstorm can shut down residential communities for days.

With files from The Canadian Press and The Associated Press