Millions of residents prepare for what has been reported to be the biggest storm ever to hit the mainland United States.

Hurricane Sandy is continuing to head towards the US East Coast as residents make last-minute preparations.

Sandy could be the biggest storm to hit the US mainland when it comes ashore on Monday night, bringing strong winds and dangerous flooding to the East Coast, from the mid-Atlantic states to New England, forecasters said on Sunday.

The storm could have a brutal impact on major cities in the target zone such as Boston, New York, Washington, Baltimore and Philadelphia, in one of the most densely populated regions of the country.

New York City’s subway, bus and train services were suspended on Sunday evening, bringing the country’s financial centre to a virtual standstill.

Michael Bloomberg, New York mayor, also ordered public schools to close on Monday and said that areas of the city from City Island to Coney Island to Battery Park City were under mandatory evacuation.

“We are ordering the evacuation for the safety of the approximately 375,000 people who live in these areas,” he said.

The hurricane has also reportedly forced the evacuation of tall ship HMS Bounty, a replica of the ship famed for the 1789 mutiny.

US Coast Guard officers told reporters the 17-member crew of the training ship, used in the Pirates of the Caribbean movies, managed to get on board two life-rafts. The Coast Guard has dispatched aircraft to bring the crew to safety.

The crew had reportedly decided to abandon ship, approximately 145km off the North Carolina coast, after taking on water and losing communications and propulsion. The vessel was about 250km west of the eye of the hurricane.

‘Life-threatening’ storm

Al Jazeera’s Kristen Saloomey, reporting from New York, said the entire East Coast was preparing for the hurricane.

“New York is expected to catch the brunt of the flooding … the National Hurricane Centre has said that the storm surge flooding could be life-threatening.”

Trading on the floor of major Wall Street exchanges will be suspended on Monday, but online operations will continue, allowing business to continue almost as usual.

US East Coast braces for Hurricane Sandy

The US government has estimated the storm could affect 50 million people, and the storm has already been disrupting transportation systems.

President Barack Obama said on Sunday that Sandy was a “serious and big storm” and called on East Coast residents to heed the orders of state and local officials to protect themselves from its onslaught.

Obama, speaking after a briefing at the federal government’s storm response centre in Washington, said officials had assured him that they had all the resources they needed in place.

He stressed that “it is important for us to respond big and to respond fast” to the hurricane’s onslaught.

“We’re going to cut through red tape and we’re not going to get bogged down in a lot of rules,” he said.

Obama is having to balance both his re-election bid and his efforts to stay on top of the storm’s impact – just nine days before election day.

More than 700 flights, both domestic and international, were cancelled on Sunday and nearly 2,500 more were cancelled for Monday, FlightAware.com said.

By 7am ET (1100GMT), more than 1,850 people had subscribed to a special Reddit thread, set up to share information and tips between internet users for the best ways to get through the storm.

Google is also hosting a live crisismap, featuring locations and capacities of emergency shelters, localised weather reports and satellite imagery.

Officials at the US Nuclear Regulatory Commission are monitoring effects of the storm on more than a dozen nuclear power stations in the affected area.

“Because of the size of it, we could see an impact to coastal and inland plants,” an NRC spokesman told Bloomberg News.

New Jersey’s Oyster Creek nuclear plant, the oldest operating nuclear power plant in the United States, is in the projected path of Hurricane Sandy. Officials say the facility, of a similar design to Fukushima’s No.1 reactor, is currently shut down for refuelling, but are keeping a watchful eye for potential flooding.

Hybrid ‘super storm’

Forecasters say Sandy is a rare, hybrid “super storm” created by an Arctic jet stream wrapping itself around a

tropical storm, possibly causing up to 30cm of rain in some areas, as well as heavy snowfall inland.

“The size of this alone, affecting a heavily populated area, is going to be history making,” said Jeff Masters, a hurricane specialist who writes a blog on Weather Underground .

Harvard University, in Cambridge, Massachusetts, cancelled all classes in what was understood to be the first time in 40 years, and New Jersey casinos were ordered to close.

Al Jazeera’s John Terrett reports from the Delaware coast

New Jersey officials have shut down the state’s bus and rail systems, and emergency officials warned of widespread power outages that could last for days.

On its current projected track, Sandy is most likely to make landfall in the New York/New Jersey area and head inland to Philadelphia and Pennsylvania, forecasters said.

Forecasters at the National Hurricane Centre in Miami said the storm’s impact would be felt far from the centre.

While Sandy’s 120kph winds are not overwhelming for a hurricane, its width makes it exceptional. Hurricane-force winds extend 280km from its centre, while its lesser tropical storm-force winds span 1,670km in diameter.

It was not expected to strengthen, but was expected to broaden.

At high tide, the storm could bring a surge of seawater up to 3.4m above normal levels to Long Island Sound

and New York Harbour.

“Given the large wind field associated with Sandy, elevated water levels could span multiple tide cycles, resulting in repeated and extended periods of coastal and bayside flooding,” the forecasters said.

Westward turn

Sandy was centred about 685km southeast of New York City on Monday morning.

The storm has pushed seawater up over the barrier islands, known as the Outer Banks, off North Carolina.

Sandy has been moving over the Atlantic parallel to the US coast at about 17kph, but was forecast to make a tight westward turn towards the US coast on Sunday night.

Tropical storm conditions were spreading across the coast of North Carolina on Sunday morning and gale-force winds are forecast to begin affecting Washington, New York and southern New England later on Monday.

Sandy has killed at least 66 people as it made its way through the Caribbean islands, including 51 in Haiti, mostly from flash flooding and mudslides, according to authorities.

Click through our gallery for more photos, as millions of US residents brace for the storm: