NEW YORK — Superstorm Sandy grounded more than 15,000 flights across the Northeast and the globe, and it could be days before some passengers can get where they’re going.

According to the flight-tracking service FlightAware, more than 6,000 flights were canceled on Tuesday. That brings the tally of flights canceled because of the storm to more than 15,000. By early Tuesday morning, more than 500 flights scheduled for Wednesday also were canceled.

The three big New York airports were closed on Tuesday by the Port Authority of New York and New Jersey. Stewart International Airport remained open, but airlines had suspended operations there.

New York has the nation’s busiest airspace, with about one-quarter of all U.S. flights traveling to or from there each day. So cancelations here can dramatically impact travel in other cities.

Delays rippled across the U.S., affecting travelers in cities from San Francisco to Atlanta. Others attempting to fly out of Europe and Asia also were stuck.

Narita, the international airport near Tokyo, canceled 11 flights Tuesday — nine to the New York area and two to Washington, D.C. All Nippon Airways set up a special counter at Narita to deal with passengers whose flights had been canceled.

Hurricane Sandy converged with a cold-weather system and made landfall over New Jersey on Monday evening with 80 mph winds. The monstrous hybrid of rain and high wind — and even snow in some mountainous inland areas — killed at least 16 people in seven states, cut power to more than 6 million homes and businesses from the Carolinas to Ohio, caused scares at two nuclear power plants and stopped the presidential campaign cold.

The storm was forecast to head across Pennsylvania before taking another sharp turn into western New York by Wednesday morning, bringing heavy rain and local flooding.

The flight cancelations surpassed those of a major winter storm in early 2011 that forced 14,000 flights to be scrapped over four days.

Even if storm damage is minor it could be a week before operations are normal at major East Coast airports, said Angela Gittens, director general of the Airports Council International, a trade group for airports worldwide.

“The storm has such a wide swath and so many major airports are involved that it’s going to take some time (to recover) because those airplanes are so far away,” said Gittens, who served as aviation director at Miami International Airport Dade during several hurricanes from 2001 to 2004.

JetBlue Airways Corp. canceled 1,200 flights for Sunday through Tuesday. The airline is hoping to resume flights at its Kennedy airport hub Wednesday, but is worried about flooding of the airport’s runways since they are all basically at sea level and near bodies of water, according to Rob Maruster, the company’s chief operating officer.

Delta Air Lines Inc. has canceled 2,100 flights over the three days. American Airlines has scrapped 1,000 flights, including 260 on regional affiliate American Eagle.

The impact on airline’s bottom lines is unclear. Many of the customers on flights currently being canceled will reschedule later on, so the airlines will still collect the fares.

Travelers overseas could wait days to get to the East Coast of the U.S.

Frankfurt airport canceled 12 incoming and nine outgoing flights because of the storm, adding to 12 it scrapped on Monday. Spain’s biggest airports in Madrid and Barcelona axed 19 flights, on top of 13 canceled the day before.

British Airways cut another 11 return flights to and from the East Coast on Tuesday, adding to 20 on Monday, when London’s Heathrow airport canceled a total of 59 flights to and from the U.S.

Air India said its daily flights to Newark and JFK had been halted since Sunday.

South Korea’s Korean Air said it canceled three flights to New York and one flight to Washington on Monday and Tuesday. Asiana Airlines canceled its Tuesday flight to New York. Its Monday flight to JFK was delayed by 26 hours, then was postponed again by another 26 hours.

Hong Kong’s Cathay Pacific Airways had canceled six New York flights by Tuesday. The airline said another New York flight via Vancouver will only go as far as the Canadian city.