The east coast of the United States is preparing for what weather forecasters expect to be one of the biggest storms ever to hit the mainland.

Hurricane Sandy is moving up the Atlantic coast and is expected to join with two winter storm systems. Forecasters are calling this a hybrid “superstorm,” bringing damaging winds, heavy rains, flooding and snow in some areas. They expect it to span some 1,200 kilometers and affect up to 60 million residents starting late Monday.

The hurricane already has winds of 120 kilometers per hour with higher gusts extending outward of up to 165 kilometers from the center.

Authorities are urging citizens to make sure they stock up on drinkable water, canned food and batteries, and be prepared to spend days without power.

New York, Pennsylvania, Maryland, Virginia, North Carolina and the nation's capital, Washington, have all declared states of emergency. Authorities in Delaware state have ordered some mandatory evacuations. The mayor of New York City has closed the school system of more than one million students on Monday and ordered the evacuation of some low-lying areas.

White House officials say President Barack Obama has told federal emergency workers to get ready to move into action when storm-battered states call for help. He has cancelled some campaign stops to remain at the White House and monitor the storm.

His Republican challenger, former Governor Mitt Romney, also cancelled campaign events in the critical battleground state of Virginia because of the storm.

Hurricane Sandy tore through the Caribbean region days ago, killing some 60 people in the Bahamas, Cuba, Jamaica and Haiti.