Mayor Michael Bloomberg said Monday night that the surge was expected to recede by midnight, after exceeding an original expectation of 11 feet.
"The worst of the weather has come," he said. He said New Yorkers were inundating the 911 system and getting stranded in cars, and urged people to stay put until the storm passed.
"You have to stay wherever you are. Let me repeat that. You have to stay wherever you are," he said.
Shortly after the massive storm made landfall in southern New Jersey, Consolidated Edison cut power deliberately to about 6,500 customers in downtown Manhattan to avert further damage. Then, huge swaths of the city went dark, losing power to 250,000 customers in Manhattan, Con Ed spokesman Chris Olert said.
New York University's hospital lost backup power, Bloomberg said.
The storm had only killed one New York City resident by Monday night, a man who died when a tree fell on his home in the Flushing section of Queens.