US emergency officials braced for the potentially massive impact of a so-called "Frankenstorm" Sunday as Hurricane Sandy lumbered north in the Atlantic Ocean, poised to hit the eastern seaboard with torrential rains and gale-force winds.

The superstorm was expected to make landfall somewhere between Virginia and Massachusetts early Tuesday, possibly causing chaos during the frenzied last days of campaigning before the November 6 US presidential vote.

As it churned in a northeasterly direction, the massive weather system was at category one strength, the lowest-level hurricane on the five-tiered Saffir-Simpson scale, with maximum sustained winds of 75 miles (120 kilometers) per hour, the National Hurricane Center (NHC) said.

The center said that while little change in strength was anticipated for Sandy, which was now located 260 miles (420 kilometers) south-southeast of Cape Hatteras, North Carolina, it was "expected to remain a large and powerful until it crosses the coastline."

Forecasters at the National Weather Service warned the storm would "result in significant impacts along coastal North Carolina" beginning late Saturday.

But emergency officials were far more worried about what could happen farther north.

"This is a large storm that is forecasted to impact the Mid-Atlantic and other parts of the East Coast with strong winds, coastal flooding, inland flooding, rain and snow," said Craig Fugate, head of the US Federal Emergency Management Agency.

Sandy's likely collision early next week with a seasonal "nor'easter" weather system was predicted to super-charge the storm, dragging it to the west, where it is expected to slam into the eastern states of Virginia, West Virginia, Pennsylvania, New York, New Jersey, Connecticut, Massachusetts and even inland Ohio.

Alex Sosnowski, an expert senior meteorologist for Accuweather.com, called Sandy "an extremely rare and dangerous storm," menacing 60 million people, that "could lead to billions of dollars in damage."

Taking the dire predictions to heart, residents were bracing for huge tidal surges, power outages, inland flooding and even heavy snowfall on high ground far from the coast.

"Sandy will be more like a large nor'easter on steroids," Sosnowski wrote.

It could have the strength of a category one or two hurricane, he explained, but with powerful winds extending out hundreds of miles from the center.

In Delaware, Governor Jack Markell issued an evacuation order, urging coastal residents and those in flood-prone areas to leave their homes to stay safe.

"Please take this evacuation order seriously. It will help save lives of both residents and first responders," he said in a message on Twitter.

"Gale force winds are expected to arrive along portions of the Mid-Atlantic coasts by late Sunday or Sunday night and reach Long Island and southern New England by Monday morning," the NHC warned. "Winds to near hurricane force could reach the Mid-Atlantic states including Long Island by Monday."

Train provider Amtrak, meanwhile, announced it was canceling some service on Sunday, including two trains on the popularroute between Washington and New York.

President Barack Obama was briefed by top emergency officials Saturday, the White House said, and governors declared states of emergency in Maryland, New York, New Jersey, Connecticut, Pennsylvania, Virginia, the US capital Washington and a coastal county in North Carolina.

The president has also canceled two campaign events early next week to monitor developments related to Sandy.

The mayor of New York, Michael Bloomberg, told reporters Saturday evening that the latest trajectory showed the storm hitting the Maryland and Delaware areas to the south of the city and that, for the moment, no evacuations were being ordered.

Meanwhile, concern was also mounting that storm damage and power outages could have a major impact on voter turnout, polling station readiness and last-minute campaigning by Obama and his Republican rival Mitt Romney.

Meteorologists have nicknamed the unusual confluence of weather patterns a "Frankenstorm" because it is due to hit just before Halloween on October 31 and is composed of parts from different sources, as was Frankenstein's monster.

The powerful hurricane earlier claimed 11 lives in eastern Cuba, including several people who died in the rubble of collapsed buildings.

On Wednesday, Sandy unleashed its wrath on Jamaica, where one person died, and on Haiti, where 44 people were killed, according to an updated official toll.

Two people were reported dead in the Dominican Republic and one in the Bahamas.

burs-nss-vlk/mdl/mk/jhb