The eastern part 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 from the north to form what forecasters are calling a hybrid “superstorm” spanning some 1,200 kilometers, affecting up to 60 million residents.

Major cities preparing for the impact of the storm include Washington, Baltimore, New York, Philadelphia and Boston. Watches and warnings are posted up and down the U.S. east coast, where Hurricane Sandy is expected to make a direct hit – somewhere – late Monday.

Several states can expect damaging winds, heavy rain and floods, with snow in some areas.

Sandy has winds of 120 kilometers per hour with higher gusts. Hurricane-force winds extend outward 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.

Washington, New York, Pennsylvania, Maryland, Virginia and North Carolina have declared states of emergency. Delaware has ordered mandatory evacuations for some areas of the state.

The White House says President Barack Obama has told federal emergency officials 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.

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