While still at sea, Hurricane Sandy already is causing widespread problems for millions of travelers, with mass transit shutdowns ordered in New York, New Jersey and Pennsylvania, Amtrak cancellations and more than 6,800 flights canceled.
New York Gov. Andrew Cuomo on Sunday ordered New York City's transit service to suspend bus, subway and commuter rail service in advance of the massive storm expected to hit the eastern third of the United States late Monday.
The system started shutting down shortly after 7 p.m. on Sunday. The last buses ran at 9 p.m.
"The transportation system is the lifeblood of the New York City region, and suspending all service is not a step I take lightly," Cuomo said. "But keeping New Yorkers safe is the first priority, and the best way to do that is to make sure they are out of harm's way before gale-force winds can start wreaking havoc on trains and buses."
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The city's mass transit system is the nation's largest. The subway alone has a daily ridership of more than 5 million.
"The MTA (Metropolitan Transit Authority) proved it can suspend service in an orderly manner when it did so last year for Tropical Storm Irene, and we have refined our Hurricane Plan since then to help us prepare for Hurricane Sandy," said MTA Chairman and CEO Joseph J. Lhota. "This storm will batter the MTA, but the precautions we take now will allow us to recover much more quickly."
"The New York City subway system will begin to curtail service after 7 p.m., and the New York City bus system within the following two hours," the MTA said in a statement. "Metro-North Railroad and the Long Island Rail Road will start their final trains by 7 p.m. Subway and railway stations will be closed after the last trains.
"Customers who need to travel today should do so as soon as possible and not wait until the last train or bus is departing. Anyone who does not leave for their destination before 7 p.m. runs the risk of being stranded when service is suspended. New York City Transit, Metro-North and the LIRR will cross-honor each other's passes today to speed the process of returning customers to their homes."
According to an MTA spokesman, the shutdown will take about eight hours to complete. This process includes the removal of electrical components in the subway that would be affected in case of flooding. Workers are preparing for that possibility, the spokesman told NBC News.
The East River ferry service was suspended, and the Staten Island Ferry will stop running at 8 p.m., New York Mayor Michael Bloomberg said in a press conference Sunday.
New Jersey Gov. Chris Christie ordered all of the state's bus, rail and light rail to begin a gradual shutdown at 4 p.m. ET, continuing through 2 a.m. Monday. The Atlantic City Rail Line will also suspend operations then.
In metropolitan northern New Jersey, PATH train service and stations also were to be shut down at 12 a.m. Monday.
Metro-North Railroad, which runs service between New York City and its northern suburbs in New York and Connecticut, will suspend service beginning at 7 p.m. Sunday, NBC affiliate WVIT reported.
The Southeastern Pennsylvania Transportation Authority (SEPTA) announced Sunday it would be suspending its service starting at about 12:30 a.m., and anticipated the shutdown would last through Monday.
The D.C.-area transit system said most of its preparations for Hurricane Sandy are complete and added there are no announced changes to Metrorail or Metrobus service as of 11:00 a.m. Sunday.
According to FlightAware.com,the most heavily affected hub was Newark, N.J., with more than 265 cancellations on Sunday. In total, 1,251 flights to, from or within the United States were canceled Sunday, FlightAware.com said. More than 5,500 flights scheduled for Monday were canceled.
Major airlines are offering waivers to customers who wish to reschedule their flights without paying the typical fee of up to $150. To cancel a ticket, passengers should call the airline.
Don Morelli, a meteorologist with WSI, a sister company of The Weather Channel, said major flight delays and airport closings were likely to continue through Tuesday.
"The criteria for closing an airport is around 58, 60 miles an hour, which is easily going to be reached for much of the major hubs from D.C. northward to New York City and even into Logan (in Boston)," Morelli said. "Major delays (are) going to be very, very widespread right through mid-week, so [it?s] not a good week to be traveling across the Northeastern U.S."
Airlines started moving planes out of airports to avoid damage, CBS News reported.
Port Authority of New York and New Jersey spokesman Anthony Hayes told NBC News that New York City-area airports remain open despite the flight cancellations. The decision to cancel flights comes from the airlines directly, he said, not from the Port Authority or the airport.
The Port Authority is encouraging travelers to check their flight status with the airline before heading to the airport.
Amtrak also announced that all Acela Express, Northeast Regional, Keystone and Shuttle services are canceled for Monday. Additionally, Empire Service, Adirondack, Vermonter, Ethan Allen and Pennsylvanian train services are also suspended, along with overnight services to and from the East Coast, according to a press release.
Service between Chicago and Washington D.C., Miami and New York, and Washington D.C. and New York is on the list of cancellations announced Saturday morning.
Amtrak said in a press release that passengers who have paid for their tickets but choose not to travel due to the service disruption can receive a refund or a voucher for future travel. Some tickets booked online that have not yet been printed can be modified or canceled, the press release said.
Amtrak said they will be contacting passengers who have provided information in their reservations, but encouraged customers to monitor alerts on their website.
In town for a friend's wedding, Lori Wolfman waited in a long line to change her tickets to an earlier train at New York's Penn Station, CBS News reported. Wolfman and her husband were supposed to be on a 3 p.m. Washington-bound train, but were exploring their options.
"We'll get on anything," she told CBS.
NBC News' Becky Bratu and Tom Costello and the Associated Press contributed to this report.