Residents rushed to moor boats, harvest crops and sandbag boardwalks as the US Eastern Seaboard braced for a rare megastorm that experts said would wreak havoc for several days.

Meteorologists expected Hurricane Sandy to pack high winds, heavy rain, extreme tides and maybe snow beginning early Sunday, peaking with the storm’s arrival on Tuesday.

“It’s looking like a very serious storm that could be historic,” said Jeff Masters, meteorology director of the forecasting service Weather Underground.

With a rare mix of three big merging weather systems over a densely populated region, experts predict at least US$1 billion in damage.

Sandy, having blown through Haiti and Cuba and leaving 43 dead across the Caribbean, continues to barrel north as the lowest category hurricane. A wintry storm is moving across the US from the west. And frigid air is streaming south from Canada.

If they meet Tuesday morning around New York or New Jersey, as forecasters predict, they could create a big, wet mess that settles over the nation’s most heavily populated corridor and reaches as far west as Ohio.

Government forecasters said there is a 90 per cent chance up from 60 per cent two days earlier that the East Coast will get pounded.

The National Oceanic and Atmospheric Administration said Friday that wherever the storm comes ashore, there will be 254 millimetres of rain and extreme storm surges. Up to 0.6 metres of snow should fall on West Virginia, with lighter snow in parts of Ohio and Pennsylvania.

“It’s going to be a long-lasting event, two to three days of impact for a lot of people,” said James Franklin, forecast chief for the National Hurricane Center.

In the northeastern state of New Jersey, officials told people to be prepared for several days without electricity. Jersey Shore beach towns began issuing voluntary evacuations and protecting boardwalks. Atlantic City casinos made contingency plans to close, and officials advised residents of flood-prone areas to stay with family or be ready to leave. Airlines said to expect cancellations and waived change fees for passengers who want to reschedule.

Some have compared the tempest to the so-called Perfect Storm that struck off the coast of New England in 1991, but that one hit a less populated area.

“The Perfect Storm only did $200 million of damage and I’m thinking a billion” this time, Masters said. “Yeah, it will be worse.”

Late on Friday, Sandy was about 145 kilometres north of Great Abaco Island in the Bahamas and 635 kilometres south-southeast of Charleston, South Carolina. It was just above the threshold for being a hurricane, with maximum sustained winds of 120 kph, and was moving north at 11 kph.