Powerful winds buckled a crane on a New York skyscraper, giving an alarming warning of the danger from Hurricane Sandy as authorities tried desperately to persuade people in high-risk areas to get to safety.

With power cuts already hitting as winds strengthened and sea levels rose, police toured flood-threatened districts of the New York region almost begging people to clear out. But tens of thousands of hurricane refuseniks resisted.

With America's biggest city at a near standstill ahead of a predicted storm surge of up to 11 feet (3.5 meters), police went to several towns and districts with loud speakers and special buses trying to persuade people to move.

Authorities issued a mandatory evacuation order for 375,000 people but the vast majority decided to brave out Sandy, which some experts said could be the most powerful storm in more than seven decades.

Only 3,000 people, with 73 pets, had moved into the 76 emergency shelters opened for the storm, New York Mayor Michael Bloomberg said.

Malcolm Smith, a Democratic member of the state senate, estimated that 80 percent of inhabitants of Rockaway Beach, a seaside town where flooding started before the hurricane made landfall, had decided to stay put.

"They need to pack up their families and move away," Smith said.

But Bloomberg said it may be too late however as wind speeds and seas rose.

"Conditions are deteriorating very rapidly and the window for getting out safely is closing," Bloomberg told a press conference. "It's getting too late to leave."

New York state governor Andrew Cuomo said the latest flood predictions were "troublesome" and criticized people who went to the beach to take pictures of the crashing waves.

Manhattan streets were mainly empty as rains fell and winds increased. The New York Stock Exchange ordered an emergency closure for the first time since the September 11, 2001 attacks. All subway trains and buses were halted at least until Wednesday.

Authorities ordered two of the main Manhattan road tunnels and nearly all bridges off the island to close as winds became more dangerous. New York state also called up an extra 1,000 National Guardsmen on top of 1,100 mobilized Sunday.

Gale force winds buckled a crane on top of a 90-story luxury apartment block which was left dangling as the storm intensified.

Police and fire services cleared streets and some other buildings around the building, close to Central Park, which was designed by award-winning French architect Christian de Portzamparc.

No casualties were immediately reported, though some witnesses said parts of the crane had fallen into the street from the 1,004-foot (306-meter) skyscraper, which is due to be finished next year.

Schools and landmark attractions such as the Empire State Building were all closed. Hardly a car ventured onto the streets.

Only the hardiest store-owners stayed open. Most supermarkets had been stripped of batteries, pocket lamps, bread and water amid widespread fears of power cuts.

David Blythe, an official with an international student exchange organization, lives in Brooklyn but booked himself into a Manhattan hotel. "I have meetings I could not miss," he said as he ate breakfast in one of the rare eateries open.

Albert Mustaj, a doorman at The Caroline, an elegant apartment block on 23rd Street, said all staff at the building had been asked to stay for three days. But he was not nervous. "I come from Montenegro, I've seen worse," he said.

Candace Ruland, a 67-year-old inhabitant of the Battery Park district, said she left for Hurricane Irene last year. "I went uptown and I had a nice dinner with a lot of wine. This year, I just decided to stay," she said.