LOS ANGELES (MarketWatch)—New York City workers were working to protect the country’s largest public-transit system and New Jersey declared a state of emergency as monster Hurricane Sandy churned up the Eastern Seaboard toward landfall.

Tens of millions of on-edge residents awaited what could be the worst storm in the region’s history as governments, businesses and citizens continued to make emergency preparations for torrential rain, high winds and flooding.

Hurricane Sandy's projected path as of Saturday morning.

Officials in the East, New England and the Midwest were taking preparatory steps ahead of the storm, which was dubbed “Frankenstorm” by weather forecasters because Hurricane Sandy could collide with a cold front coming from the West and with cold air streaming down from Canada.

Sandy could grow into a fiercer storm by tapping into the energy of the two other weather systems.

“Definitely, tens of millions will see effects from Sandy, and some of the heaviest effects will be, unfortunately, from I-95 eastward to the coastline,” including densely populated metro areas such as New York City, Washington, D.C. and Philadelphia, said Alan Reppert, a senior meteorologist at AccuWeather.com, on Saturday. Read: Hurricane Sandy: What homeowners need to know.

“We’re looking at impact of greater than 50 to 60 million people,” The Associated Press quoted Louis Uccellini, head of environmental prediction for the National Oceanic and Atmospheric Administration, as saying.

As Hurricane Sandy barreled north from the Caribbean—where it left nearly five dozen dead—to meet two other powerful winter storms, experts said it didn’t matter how strong the storm was when it hit land: The rare hybrid storm that follows will cause havoc over 800 miles from the East Coast to the Great Lakes.

“This is not a coastal threat alone,” said Craig Fugate, director of the Federal Emergency Management Agency. “This is a very large area.”

On Sunday, the storm was packing 75-mph winds and was expected to create a significant storm surge, a 2 a.m. Eastern update from the National Hurricane Center said.

Sandy was centered 260 miles south-southeast of Cape Hatteras, N.C., and hurricane-force winds extended 105 miles out from the center, the NHC reported. Tropical-storm-strength winds extended as far as 520 miles, the agency said.

Gale-force winds were expected to arrive along portions of the mid-Atlantic coast by late Sunday or Sunday night, and reach Long Island and Southern New England by Monday morning, said the NHC update. Click here for National Hurricane Center.

“There will be school closures, travel will be messed up for days and major airports will be closed,” said Henry Margusity, a senior meteorologist with AccuWeather, on Saturday. “This could be a disaster of biblical proportions—a multibillion-dollar disaster.”

Under a worst-case scenario, New York could face the most intense storm in its history. See related story by meteorologist Eric Holthaus on how storm has potential to break weather records.

The storm could bring in high winds and heavy rain to New York City that could make operating transit lines, tunnels and bridges dangerous. Nearly 15 million people in a 5,000-square-mile area stretching from New York City through Long Island, southeastern New York state and Connecticut.

There were no plans to mandate evacuations in low-lying areas of New York City, said Mayor Michael Bloomberg at a news conference Saturday afternoon, but officials will continue to monitor the situation. See: New York prepares for worst from Sandy.

Before noon Eastern on Saturday, New Jersey Gov. Chris Christie declared a state of emergency and urged residents not to brush off warnings from weather forecasters about the severity of the storm. He ordered mandatory evacuations in the state’s coastal areas, including casino center Atlantic City, by late Sunday afternoon.

Sandy to slam Northeast

“We have to be prepared for the worst,” he said, adding that if the storm hits as hard as predicted, areas of the state could be without power for seven to 10 days. Newark, N.J.-based PSE&G PEG, +0.82% started to bring in extra workers to handle any power outages. The company said it’s requested more than 1,300 linemen and 600 tree contractors from utilities in other states to assist its crews.

New York Gov. Andrew Cuomo declared a state of emergency for the entire state Friday evening. State of emergencies have also been declared in Maryland, Virginia, sections of North Carolina and in the D.C. area.

Parts of the Delmarva Peninsula, southern New Jersey, eastern Maryland and southern Pennsylvania could see more than 8 inches of rain starting Sunday night through the heaviest rainfall on Monday night, said Reppert. Snow is projected to fall in the West Virginia mountains, he added.

Hurricane Sandy also forced schedule changes on the campaign trail, with time running out for candidates to drum up support before the general election on Nov. 6. Vice President Joe Biden canceled Saturday plans to appear in Virginia Beach, Va., and Republican presidential candidate Mitt Romney will not hold a rally in the same coastal city on Sunday. President Barack Obama’s campaign switched his departure for Florida to Sunday night from Monday. He appeared in New Hampshire on Saturday.

Wall Street also braced for Hurricane Sandy.

Rich Adamonis, a spokesman for the New York Stock Exchange US:NYX, said Friday contingency plans were being drawn up.

A Nasdaq OMX Group Inc. NDAQ, -3.18% spokesman said Friday the electronic equities exchange plans to continue to operate despite the approach of Hurricane Sandy early next week.

“We have fully rehearsed business continuity plans for all critical operations including facilities, market operations and key staff and stand ready to implement should a situation necessitate,” said Nasdaq spokesman Ryan Wells.

Last year, the Nasdaq and the NYSE operated even after Hurricane Irene shut down much of the region’s transportation infrastructure.

The New York Mercantile Exchange said it has plans in place to make sure its markets continue to function.

Stanley Sicinski looks at storm surf before sunrise Saturday in St. Augustine Beach, Florida, as Tropical Storm Sandy passes by. Reuters

“We will continue to monitor the situation and will notify customers, market participants and our employees as appropriate,” emailed Damon Leavell, a spokesperson for the CME Group CME, -1.66% , which owns the NYME, where crude-oil futures and other commodities are traded.

“We have no immediate plans to close the exchange,” said Leavell. He added that CME’s Globex platform, the exchange’s electronic trading system, is based in the Midwest, with backup systems scattered in varying locations.

In the commodity markets, New York Harbor RBOB gasoline futures RBX22, rose 2 cents to $2.70 a gallon. Andy Lipow, president of Lipow Oil Associates LLC in Houston, said futures are reflecting concerns about the potential for supply disruption.

“People won’t see much of an impact on the retail level, but it could slow down the drop of gasoline prices that we’ve seen,” he said.

While it could cause refineries to pare output, the storm won’t have any impact on the Gulf of Mexico. “The impact of the storm will be localized,” Lipow said. Read about oil industry bracing for Hurricane Sandy.

Conditions are similar to the weather patterns that led to the infamous “perfect storm” that battered New England in 1991, Brian McNoldy, a research associate at the University of Miami, said. Read about stores stocking up for hurricane.

Sandy arrives little more than a year after Hurricane Irene caused a historic shutdown of the New York City subway system and inflicted an estimated $15 billion in damage.