President Obama has cut short his holiday warning Hurricane Irene will be a "historic" storm, as low lying parts of New York are evacuated and public transport shut down.

Please wait while this video loads. If it doesn't load after a few seconds you may need to have Adobe Flash installed.

Authorities in New York City have ordered a mandatory evacuation of all low-lying areas before Hurricane Irene hits.

Some 55 million people are potentially in Irene's path, from the Carolinas to Cape Cod on the East Coast, and hundreds of thousands are evacuating coastal communities as cities including New York brace for the storm to hit.

The escalating situation prompted President Barack Obama and his family to cut short their vacation and return to the White House on Friday, before Hurricane Irene hits the U.S. East Coast, the White House said.

"In the mind of the president, he felt it was prudent for him to be at the White House this evening," said White House spokesman Josh Earnest. Obama had been scheduled to end his nine-day family vacation in Massachusetts on Saturday morning.

New York Mayor Michael Bloomberg said the evacuation - estimated at more than 250,000 people - could begin when shelters opened this evening.

"We've never done a mandatory evacuation before and we wouldn't be doing it now if we didn't think this storm had the potential to be very serious," Bloomberg said.

Earlier, New York Governor Andrew Cuomo said the city's mass transit system, which serves eight million passengers a day, will be shut at approximately noon on Saturday.

The shutdown includes the New York subway, buses and commuter lines that serve the surrounding suburbs. The loss of the public transport network could complicate any possible evacuations.

Governor Cuomo also said the New York Army and air National Guard were being deployed to support authorities preparing for the hurricane.

Please wait while this video loads. If it doesn't load after a few seconds you may need to have Adobe Flash installed.

New York bridges will be shut down if winds exceed 60mph (96kph), including George Washington and Tappan Zee bridges.

President Barack Obama said that the 55 million Americans in the path of the huge hurricane should start preparations now for the storm.

In a statement from his holiday, the President said: "All indications point to this being a historic hurricane."

All indications point to this being a historic hurricane. President Barack Obama

The first signs of the storm are already being felt on the North and South Carolina coasts. Waves of between six and nine feet have been reported and thousands of people have already lost power.

The eye of the storm is expected to reach the Carolinas late on Friday night local time, before heading up the coast to New York over the weekend. Forecasters expanded the hurricane warning area from North Carolina to Sandy Hook, New Jersey, south of New York City.

Craig Fugate, director of the Federal Emergency Management Agency, warned that the hurricane could affect an unusually large area.

He said: "This is one of the largest populations that will be impacted by one storm at one time. We're going to have damages, we just don't know how bad."

Avon, North Carolina (Reuters)

US Homeland Security Secretary Janet Napolitano warned on Friday that residents could expect extensive power cuts when the hurricane hits. Operators of oil, natural gas and power infrastructure in the densely populated US Northeast activated emergency plans on Friday and warned of potential supply disruptions.

Pipeline and terminal operator Magellan Midstream partners was shutting petroleum terminals in North Carolina and Virginia on Friday.

According to an astronaut on the International Space Station Hurricane Irene looks "terrifying" from space.

Nasa astronaut Mike Fossum said: "We saw a big change in the structure of the storm over the several days that we've watched her, especially yesterday. You know that is a powerful storm and those are never good news when they're headed your way."

Residents prepare for Hurricane Irene (Getty)

New York fears

New Yorkers living in low-lying areas have been told to think about evacuating on Friday before Hurricane Irene hits the city of 8.4 million people, Mayor Michael Bloomberg said on Thursday.

In New Jersey, 750,000 people have been told to evacuate. Atlantic City casinos have been told to suspend gaming at noon on Saturday, although hotel guests who have been stranded because of transport issues will be allowed to stay. Potential looters have been warned off with extra security and surveillance.

After hitting North Carolina, Irene is expected to weaken to a still-dangerous Category 2 storm on the five-step Saffir-Simpson scale, with winds of up to 110 mph (177 kph). Its course after that will take it up the east coast and some forecast models suggest it will hit the New York area.

The American flag draped over the New York Stock Exchange (NYSE) has been removed so that it doesn't get torn down by the hurricane. Inside the building, staff are preparing a generator and extra food has been brought in. A final decision on whether to open on Monday will not be made until later in the weekend. In a worst-case scenario, New York Harbour waters could flood the low-lying downtown area.

Lou Pastina, executive vice president of NYSE, said they were concerned about the weather: "If you get a huge tidal surge the building wouldn't be occupiable. We intend to be open but Mother Nature may have other plans."

Read more: 125,000 still missing in New Orleans, five years after Katrina

The hurricane is moving particularly slowly according to expert,s and there is concern about how long it may stay over the cities and towns it strikes.

"One of my greatest nightmares was having a major hurricane go up the whole Northeast Coast," said Max Mayfield, the former chief of the National Hurricane Centre.

"This is going to have an impact on the United States economy."

North Carolina has been bracing itself for a direct hit with residents stocking up on food and water and working to secure homes, vehicles and boats.

"This is a big, bad storm," North Carolina Governor Bev Perdue said.

"We are prepared for the worst, praying for the best...we are ready."

Virginia Governor Bob McDonnell urged residents to seek shelter by Friday night, before the winds kick up.

EQECAT, a company that helps the insurance industry predict disaster damage, said Irene's forecast track represented "one of the worst case scenarios" for the United States.

Click on the image below for a photo gallery of Hurricane Irene.