NEW YORK – Hurricane Sandy unleashed its fury on the US East Coast on Monday with fierce winds and driving rain, as the mega storm shut down transportation, shuttered businesses and sent thousands scrambling to get out of flood zones.

The United Nations announced plans to close on Monday and cancelled all meetings at its headquarters in New York.

About 50 million people from the Mid-Atlantic to Canada were in the path of the nearly 1,000-mile-wide storm, which forecasters said could be the largest to hit the mainland in US history. It was expected to topple trees, damage buildings, cause power outages and trigger heavy flooding.

Residents and emergency management officials have been keeping a wary eye on the hurricane’s expected path, bracing for the impact in states like Connecticut, Delaware, Maryland, New York, New Jersey, North Carolina, Pennsylvania and Virginia.

But hours before landfall, streets were already swamped, structures destroyed and waterways transformed as the storm’s outlying sections pushed wind and water ahead of it.

The US stock market suffered its first weather-related closure in 27 years and many schools and businesses were closed in Washington, Baltimore, Philadelphia and New York.

While the centre of the storm was not expected to make landfall until Monday night near Atlantic City, New Jersey, it was already creating dangerous conditions and forcing rescue workers into action.

Off North Carolina, the US Coast Guard rescued 14 of the 16 crew members who abandoned the replica tall ship HMS Bounty, using helicopters to lift them from life rafts. The Coast Guard continued to search for the two missing crew members about 160 miles from the eye of the storm.

The US National Hurricane Center (NHC) said the Category 1 storm had strengthened as it turned toward the coast and was moving at 30 km per hour. It was expected to bring a "life-threatening storm surge," coastal hurricane winds and heavy snow in the Appalachian Mountains, the NHC said.

Forecasters said Sandy was a rare, hybrid "super storm" created by an Arctic jet stream wrapping itself around a tropical storm. Nine US states have declared a state of emergency.

With the election eight days away, President Barack Obama cancelled a campaign event in Florida on Monday in order to return to Washington and monitor the US government's response to the storm.

The president ditched plans to appear with ex-president Bill Clinton in Florida to steer a huge government relief effort as high winds and torrential rains began to lash the northeastern United States.

"This is a serious and big storm," Obama said on Sunday after a briefing at the federal government's storm response center in Washington. "We don't yet know where it's going to hit, where we're going to see the biggest impacts.

Local residents said police knocked on doors on Sunday, reminding everyone there was a mandatory evacuation. While the police took names, they allowed residents to stay at their own risk.

Transportation systems shut down in anticipation. Airlines cancelled flights, bridges and tunnels closed, and national passenger rail operator Amtrak suspended nearly all service on the East Coast. The US government told non-emergency workers in Washington, DC, to stay home.

Utilities from the Carolinas to Maine reported late Sunday that 14,000 consumers were already without power.

Agencies add:

Republican Mitt Romney also altered his plans as he tried to drive recent momentum right up to polling day on November 6, seeking to fracture Obama's "firewall" of midwestern states and deprive him of a second term.

The Republican instead canceled rallies in storm-threatened Virginia and went instead to inland Ohio, the Midwestern epicenter of the unpredictable final week battle for the White House.

He was due to spend Monday on the stump in Ohio and Iowa, though will likely tame the vehemence of his message, to avoid accusations he is playing politics while Obama hovers above the fray and shows leadership.

The storm, expected to be at its most severe on Monday and Tuesday, was the latest manifestation of the "October Surprise" -- the fabled late-campaign news event with the potential to sway the outcome of a US election.

It was expected to bring dire conditions to Virginia and also could impact other swing states including Ohio and New Hampshire, and depress early voting elsewhere.

Hurricane Sandy battering US East Coast, UN closed