White House spokesman Josh Earnest said Obama, originally due to leave Martha's Vineyard on Saturday, decided it would be more prudent to be at the White House with Irene due to hit North Carolina and the eastern seaboard.

"The president informed his team that he would like to depart Martha's Vineyard this evening to return to the White House," Earnest told reporters.

Earlier, Obama warned Americans to take immediate precautions as the "extremely dangerous" Hurricane Irene bore down on the east coast.

"I cannot stress this highly enough. If you are in the projected path of this hurricane, you have to take precautions now. Don't wait. Don't delay. We all hope for the best, but we have to be prepared for the worst."

"If you are given an evacuation order, please follow it," Obama said outside his vacation rental property on Martha's Vineyard, Massachusetts.

Irene, a category two hurricane, is forecast to make landfall Saturday in North Carolina, where residents were fleeing normally bustling beach communities and could score a direct hit on New York City.

"We are anticipating it to be a huge geographical area with lots of people impacted," warned Gail McGovern, head of the American Red Cross, at a press conference in Washington.

"From the time perspective, this could take weeks, maybe months to be able to respond to," she told reporters alongside Homeland Security Secretary Janet Napolitano and Craig Fugate, chief of the Federal Emergency Management Agency (FEMA).

The US military has confirmed that up to 98,000 National Guard soldiers will be available if needed throughout the affected regions, as Irene on Friday barreled up the US eastern seaboard.

It is expected to slam into North Carolina's Atlantic coastline as a category 2 hurricane, starting early Saturday, before roiling northward, threatening US states from Delaware to Maine.

Some 65 million people live along the path that Irene will hit in the coming days.

McGovern meanwhile cautioned that residents even far inland, such as in the US capital Washington, should be prepared for days-long power outages and possible storm surges rushing up the waterways.

"You will not be able to get everything back on quickly. A lot of rain and flooding. Strong gusty winds. Again, those impacts, well away from the coast," she said.

US authorities have readied tens of thousands of ready-meals to hand out to evacuees, with preparations being made for a million meals a day in the worst case scenario.