As tens of millions of people in the eastern third of the U.S. prepare for drenching rain and winds that could hit 80 mph from Hurricane Sandy, New York Gov. Andrew Cuomo announced that New York City will suspend its bus, subway and commuter rail service Sunday evening ahead of the storm.

"You don't want to be over panicked and overly prepared, but you want to be prudent and do what's necessary," Cuomo said, indicating that the transit system will close at 7 p.m. ET. 

Cuomo also said that bridges and tunnels in the New York area will be closed on a case-by-case basis, and 1,100 National Guard troops will be deployed to the area, including 400 on Long Island and 200 in New York City.

The city closed the subways before Hurricane Irene last year, and a Columbia University study predicted that an Irene surge just 1 foot higher would have paralyzed lower Manhattan.

New York City Mayor Michael Bloomberg also announced the closure of all city public schools for Monday and ordered mandatory evacuations of all low-lying areas. He urged residents in lower Manhattan to call 311 or visit the city's website for information on evacuation zones.

"If you don't evacuate, you are not only endangering your life, you are also endangering the lives of the first responders who are going in to rescue you," Bloomberg said.

The warning from other officials to anyone who might be affected in the storm's path was simple: Be prepared and get out of the way. The storm is expected to bring a few days of rain, high winds and possibly heavy snow.

"We're looking at impact of greater than 50 to 60 million people," said Louis Uccellini, head of environmental prediction for the National Oceanic and Atmospheric Administration.

Hurricane Sandy was headed north from the Caribbean, where it left nearly five dozen dead, to meet a winter storm and a cold front, plus high tides from a full moon, and experts said the rare hybrid storm that results will cause havoc through 800 miles from the East Coast to the Great Lakes.

Sandy was at Category 1 strength, packing 75 mph winds, about 250 miles southeast of Cape Hatteras, N.C., and moving northeast at 14 mph as of 11 a.m. Sunday, according to the National Hurricane Center in Miami. It was about 575 miles south of New York City. Waves are already battering Hatteras Island.

The storm was expected to continue moving parallel to the Southeast coast most of the day and approach the coast of the mid-Atlantic states by Monday night, before reaching southern New England later in the week.

"I've been here since 1997, and I never even put my barbecue grill away during a storm," Russ Linke said shortly before he and his wife left Ship Bottom, N.J. on Saturday. "But I am taking this one seriously. They say it might hit here. That's about as serious as it can get."

He and his wife secured the patio furniture, packed the bicycles into the pickup truck, and headed off the island.

The danger was hardly limited to coastal areas. Forecasters were far more worried about inland flooding from storm surge than they were about winds. Rains could saturate the ground, causing trees to topple into power lines, utility officials said, warning residents to prepare for several days at home without power.

States of emergency were declared from North Carolina, where gusty winds whipped steady rain on Sunday morning, to Connecticut. Delaware ordered mandatory evacuations for coastal communities by 8 p.m. Sunday.

"You never want to be too naive, but ultimately, it's not in our hands anyway," said Andrew Ferencsik, 31, as he purchased plywood and 2-by-4 lumber from a Home Depot in Lewes, Del.

New Jersey Gov. Chris Christie, who was criticized for not interrupting a vacation in Florida while a snowstorm pummeled the state in 2010, broke off campaigning for Republican presidential nominee Mitt Romney in North Carolina on Friday to return home.

"I can be as cynical as anyone," said Christie, who declared a state of emergency Saturday. "But when the storm comes, if it's as bad as they're predicting, you're going to wish you weren't as cynical as you otherwise might have been."

Up and down the Eastern Seaboard and far inland, officials urged residents and businesses to prepare in ways big and small.

In Nassau County on Long Island, County Executive Edward P. Mangano said three public shelters will be opened at 1 p.m. 

"Get your emergency kits ready and be prepared to move," he said.

In neighboring Suffolk County, a mandatory evacuation of Fire Island by 2 p.m. Sunday was ordered, with all parks to close at 6 p.m.

The town of Ocean City has ordered an evacuation of downtown residents as Hurricane Sandy heads for the Delmarva Peninsula.

Residents must leave the area south of 17th St. by 8 p.m. Sunday.

In addition, a voluntary evacuation order has been issued for residents and occupants of known low-lying areas. And Mayor Rick Meehan has closed the beach to everyone until further notice.

The town says severe flooding is expected.

Amtrak began canceling train service Saturday night to parts of the East Coast, including between Washington and New York. Airlines started moving planes out of airports to avoid damage and adding Sunday flights out of New York and Washington in preparation for flight cancellations on Monday.

Airlines also cancelled more than 3,000 flights as of Sunday morning, with hubs along the East Coast bearing the brunt of the disruptions.

According to the flight-tracking service FlightAware, 707 flights have been cancelled Sunday, with more than 265 cancellations at Newark Airport.

For Monday, 2,499 flights are cancelled, with 774 cancellations at Newark, followed by 428 at Dulles in Washington and 355 cancellations at Philadelphia.

The Virginia National Guard was authorized to call up to 500 troops to active duty for debris removal and road-clearing, while homeowners stacked sandbags at their front doors in coastal towns.

In Arlington, just outside Washington, D.C., a few shoppers strolled in and outside a Giant supermarket. Cathy Davis, 40, said the supermarket was sold out of the water she wanted to purchase, but she wasn't doing much else to prepare. She figured she would bring her outdoor furniture inside later in the day, and might make some chili.

She said the storm did lead her to decide against decorating for Halloween.

"I was like, 'eh, it will just be blown away anyway,'" she said. "What's the point."

President Barack Obama was monitoring the storm and working with state and locals governments to make sure they get the resources needed to prepare, administration officials said.

In North Carolina's Outer Banks, there was some scattered, minor flooding at daybreak Sunday on the beach road in Nags Head. The bad weather could pick up there later in the day, with the major concerns being rising tides and pounding waves.

In New Jersey, hundreds of coastal residents started moving inland. Christie's emergency declaration will force the shutdown of Atlantic City's 12 casinos for only the fourth time in the 34-year history of legalized gambling here. City officials said they would begin evacuating the gambling hub's 30,000 residents at noon Sunday, busing them to mainland shelters and schools.

The storm also forced the presidential campaign to juggle schedules. Romney scrapped plans to campaign Sunday in Virginia and switched his schedule for the day to Ohio. First lady Michelle Obama canceled an appearance in New Hampshire for Tuesday, and Obama moved a planned Monday departure for Florida to Sunday night to beat the storm. He also canceled appearances in Northern Virginia on Monday and Colorado on Tuesday.

Former sailor Ray Leonard, 85, had a bit of advice for those in the path of the storm. Leonard and two crewmates in his 32-foot sailboat, Satori, rode out 1991's infamous "perfect storm," made famous by the Sebastian Junger best-selling book of the same name, before being plucked from the Atlantic off Martha's Vineyard, Mass., by a Coast Guard helicopter.

"Don't be rash," Leonard said Saturday from his home in Fort Myers, Fla. "Because if this does hit, you're going to lose all those little things you've spent the last 20 years feeling good about."

The Associated Press contributed to this report.