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By Holly Yan, CNN

(CNN) — The repertoire of destruction caused by superstorm Sandy compounded overnight, as electrical fires and record power outages added to the misery of epic flooding plaguing the Northeast.

By early Tuesday morning, at least 6.5 million people shivered in the dark across 13 states and the District of Columbia. And Sandy claimed at least 16 lives across the United States, adding to the 67 people already killed by the storm in the Caribbean.

*Track Sandy’s path

In New York City, emergency backup power failed and 10 feet of water flooded the basement of NYU Langone Medical Center, prompting the evacuation of 260 patients. Nurses manually pumped air to the lungs of those on respirators.

Atlantic City in New Jersey became an extension of the Atlantic Ocean. Seaweed and ocean debris swirled in the knee-deep water covering downtown streets.

And in Connecticut, the emergency management office sent out an ominous tweet to trapped residents: “If u find urself surrounded by H2O, call 4 help if u can & then get 2 highest level of home. Hang a white sheet out a street side window.”

“I’ve been down here for about 16 years, and it’s shocking what I’m looking at now. It’s unbelievable,” said Montgomery Dahm, owner of the Tun Tavern in Atlantic City. “I mean, there’s cars that are just completely underwater in some of the places I would never believe that there would be water.”

More fury to come

But the weather nightmare still isn’t over yet.

Forecasters says the entire northeast corridor of the United States will bear the brunt of Sandy.

Fierce winds will blow from northern Georgia into Canada and as far west as Lake Michigan. Heavy rains will soak New England and parts of the Midwest.

And a blizzard spawned by Sandy will bring 2 to 3 feet of snow to the mountains of West Virginia by Wednesday morning.

“It’s three feet of heavy snow. It’s like concrete,” said meteorologist Reed Timmer, who is riding out the storm in Elkins, West Virginia.

Thousands of flights will remain grounded Tuesday. Federal government offices will stay closed. And it will take between 14 hours and four days to get the water out of the subway tunnels in New York City.

“The New York City subway system is 108 years old, but it has never faced a disaster as devastating as what we experienced last night,” said Joseph Lhota, chairman of New York’s Metropolitan Transportation Authority (MTA). “Hurricane Sandy wreaked havoc on our entire transportation system, in every borough and county of the region.”

A true picture of Sandy’s wrath won’t be apparent until daylight. But according to a government prediction, Sandy’s wind damage alone could result in more than $7 billion in economic loss.

Power outages spanned from Virginia to Maine.

“This will be the largest storm related outage in our history,” said Vice President John Miksad of power company Con Edison.

Roaring in

After killing 67 people in the Caribbean, Sandy made landfall Monday night in southern New Jersey, sending waves of water into major cities along the East Coast.

The iconic Manhattan skyline turned eerily dark as howling winds and rising waters from Sandy shorted power lines.

At least two dozen homes were burning in a six-alarm fire in the Breezy Point neighborhood of Queens.

Officials blame Sandy for at least 16 deaths in the United States. Several, including an 8-year-old boy in Pennsylvania, died after they were struck by a tree or tree limb. Another death was reported in Canada, where a woman was struck by flying debris — bringing the overall total to 81.

Hardik Rajput of Nassau County, New York, couldn’t believe the sight of waves crashing over the height of cars.

“To be honest, I was just stunned,” he said. “I’ve never seen that. Just to see it on the street level was astounding.”

In New York, Manhattan’s Battery Park recorded nearly 14-foot tide, smashing a record set by 1960’s Hurricane Donna by several feet.

Five hours after making landfall, Sandy still packed hurricane-force winds as it swirled about 10 miles southwest of Philadelphia.

As residents in New York and New Jersey surveyed the flooding left by Sandy, many discovered their high-rise apartment buildings are now islands.

“I am looking outside of my 6th floor apartment, and I see that a new lake has formed in the parking lot adjacent my building,” New York resident William Yaeck said. “I would be concerned, but now my building has a view of the river.”

— CNN’s Elizabeth Cohen, Ed Payne, Chandler Friedman, Amanda Watts, Eden Pontz, Ali Velshi and Henry Hanks contributed to this report.