Superstorm Sandy slammed into the US coastline and hurled a record-breaking 13ft surge of seawater at New York City on Monday.
Just before its centre reached land, the storm was stripped of hurricane status, but the distinction was purely technical, based on its shape and internal temperature.
It still packed hurricane-force wind and forecasters were careful to say it remained every bit as dangerous to the 50 million people in its path.
The National Hurricane Centre announced at 8pm on Monday that Sandy had come ashore near Atlantic City, New Jersey. The sea surged a record of nearly 13ft at the foot of Manhattan.
In an attempt to lessen damage from the storm, New York City's main utility cut power to about 6,500 customers in lower Manhattan.
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Authorities worried that seawater would seep into the New York subway and cripple it, along with the electrical and communications systems that are vital to the nation's financial centre.
As it closed in, Sandy knocked out electricity to more than 1.5 million people.
It smacked the boarded-up big cities of the Northeast corridor, from Washington and Baltimore to Philadelphia, New York and Boston, with stinging rain and gusts of more than 85 mph.
As it made its way toward land, it converged with a cold-weather system that turned into a fearsome superstorm, a monstrous hybrid consisting not only of rain and high wind but of snow.
Forecasters warned of 20ft waves bashing into the Chicago lakefront and up to 3ft of snow in West Virginia.
Hundreds of thousands of people were under orders to move to higher ground and storm damage was projected at 10 billion US dollars (£6.2 bilion) to 20 billion US dollars (£12.4 billion), meaning it could prove to be one of the costliest natural disasters in US history.
President Barack Obama and Mitt Romney suspended their campaigning with just over a week to go before Election Day.
At the White House, Mr Obama made a direct appeal to those in harm's way: "Please listen to what your state and local officials are saying.
"When they tell you to evacuate, you need to evacuate. Don't delay, don't pause, don't question the instructions that are being given, because this is a powerful storm."
The storm washed away a section of the Atlantic City Boardwalk in New Jersey. Water was splashing over the seawalls at the southern tip of Manhattan.
A construction crane atop a luxury high-rise in midtown Manhattan collapsed in high winds and dangled precariously. Residents in surrounding buildings were ordered to move to lower floors and the streets below were cleared but there were no immediate reports of injuries.
The facade of a four-story Manhattan building in the Chelsea neighbourhood crumbled and collapsed suddenly, leaving the lights, couches, cabinets and desks inside visible from the street. No-one was hurt, although some of the falling debris hit a car.
In the New York borough of Queens, police said a man was killed when a tree fell on his home - the first confirmed storm-related death in New York City.
In neighbouring Canada, police in Toronto said a woman was killed by a falling sign as high winds from the approaching superstorm whipped the city.
The major American stock exchanges closed for the day, the first unplanned shutdown since the September 11 attacks in 2001. Wall Street expected to remain closed on Tuesday. The United Nations canceled all meetings at its New York headquarters.
Authorities warned that New York City and Long Island could get the worst of the storm surge: an 11-ft onslaught of seawater that could swamp lower Manhattan, flood the subways and damage the underground network of electrical and communications lines that are vital to the nation's financial capital.
"Leave immediately. Conditions are deteriorating very rapidly, and the window for you getting out safely is closing," New York Mayor Michael Bloomberg told those in low-lying areas earlier in the day.
Consolidated Edison spokesman Chris Olert said that the power was out for most of Manhattan south of 26th Street on Monday evening.
On the east side, the power outage extended from 29th Street south. There were some scattered areas that still had electricity.
Olert said the damage stemmed from flooding and the probable loss of a transmission feeder.
The power outage was separate from a planned power cut that Con Ed did in certain lower Manhattan neighbourhoods to protect underwater systems from flood damage.
Olert said there were 250,000 customers without power in Manhattan. A customer represents a single meter, so the number of people actually affected is likely higher.
Mayor Michael Bloomberg revealed back-up power had been lost at New York University hospital and the city was working to move people out.
The mayor said that rain was tapering off in the city and the storm surge was expected to recede by midnight.
The hospital complex is near the East River in an area of lower Manhattan where flooding has been reported.
Bloomberg says a few parts of lower Manhattan still have power. He said there have been a large number of fires reported from downed power lines.