More than four million people and businesses from Folly Beach, S.C. to Portland, Maine are without power and it could take several days to restore power to those left in the dark by Hurricane Irene.
The race to restore power now will hinge on thousands of utility workers.
Getting the lights back on is an enormous job for repair crews fanning out throughout the East Coast. Irene ripped down power lines and may have flooded underground electrical wires and other equipment on the grid. Crews are still assessing the damage in states from South Carolina to Massachusetts.
Utility workers first must comb through thousands of square miles to find out what's down. Then they must start repairs.
"It's going to be several days at least for our most severely damaged areas" to get power back, said Mike Hughes, a spokesman for Progress Energy in North Carolina, which serves about 3.1 million customers.
In the South, where the storm hit first, crews have already started clearing uprooted trees and reconnecting electrical lines. Power is returning to several hundred thousand homes and businesses in the region. Utilities in southern Pennsylvania, North Carolina, Virginia and Maryland say they've restored power to more than 600,000 people as of Sunday morning.
But millions of people remain without electricity along the Eastern Seaboard.
"A number of rivers in northern New Jersey are under an extreme flood watch," said Ron Morano, a spokesman for Jersey Central Power & Light. He said the number of outages would go up.
Some of the damage will be easy to spot: a tree smashed into a power pole, for example. Other problems will be tougher to figure out. Sometimes power has been cut off with no apparent damage. That's a tougher situation because crews need to move slowly down power lines, looking for places where there is no electrical current. That can take days.
Power companies will focus on parts of their system where they can restore power to the most people at once. They'll start with massive transmission lines that supply entire counties. Then they'll deal with smashed utility poles that serve individual neighborhoods.
New York City's biggest power company, Consolidated Edison, said it was optimistic it would not have to cut electricity to save its equipment. The city escaped any vast power outages.
A nuclear reactor at Maryland's Calvert Cliffs went offline automatically when a large piece of aluminum siding blew off and hit the facility's main transformer late Saturday night. An "unusual event" was declared, the lowest of four emergency classifications by the Nuclear Regulatory Commission, but Constellation Energy Nuclear Group spokesman Mark Sullivan said the facility and all employees were safe.
After battering the East Coast on Saturday and early Sunday, Irene weakened and headed toward eastern Canada.