"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.
The rains and howling winds, some believed to reach more than 95 mph, left a crane hanging off a luxury high-rise in midtown Manhattan, causing the evacuation of hundreds from a posh hotel and other buildings. Inspectors were climbing 74 flights of stairs to examine the crane hanging from the $1.5 billion.
The facade of a four-story Manhattan building in the Chelsea neighborhood 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.
On coastal Long Island, floodwaters swamped cars, downed trees and put neighborhoods under water as beachfronts and fishing villages bore the brunt of the storm. A police car was lost rescuing 14 people from the popular resort Fire Island.