Washington/New York, Oct 29 (IANS): Millions of Americans over a 700-mile stretch across eight states up and down the East Coast prepared to meet the onslaught of approaching Hurricane Sandy and its potentially devastating impact.

President Barack Obama declared a state of emergency in the national capital as also Maryland, Massachusetts and New York as he headed back to Washington to monitor the situation from the White House after changing his campaign plans.

Washington's Metro system, all federal buildings in the city as also public schools are closed Monday.

The local government distributed sandbags to residents and businesses and authorities have kept generators ready at major intersections in case traffic lights are knocked out, Mayor Vincent Gray's office said.

Like several neighbouring states, Maryland could see as much as a foot of rain in some areas, according to the CNN Weather Unit.

Officials in Ocean City ordered all downtown-area residents to leave before 8 p.m. Sunday. A voluntary evacuation order was in place for those in low-lying areas.

In Virginia, which could alo see as much as a foot of rain according to the weatherman, sandbags were piled up inside restaurants in the Old Town section of Alexandria, along the banks of the Potomac River, in anticipation of Sandy's arrival.

In Massachusetts, Governor Deval Patrick declared a state of emergency for the Bay State, while the City of Boston announced that schools will be closed Monday. Harvard University and Harvard Kennedy School too have suspended operations for Monday.

New York's Metropolitan Transportation Authority started shutting down subway service at 7 p.m. Sunday. The city expects a slow surge of water to flood low-lying areas such as Queens, the Bronx and Battery Park in Manhattan, Mayor Michael Bloomberg said.

The Port Authority of New York and New Jersey said all its trains and stations will close at midnight amd all Port Authority Bus Terminal carriers will suspend service by early Monday morning.

Offices at United Nations headquarters in Manhattan also will be closed Monday, as will the physical trading floor of the New York Stock Exchange. Operations will continue on the company's electronic exchange.

Several other states in the Northeast including Maine, New Hampshire, Rhode Island, New Jersey, Pennsylvania, Delaware, Connecticut and North and South Carolina too declared a state of emergency and closed schools and public transport services.