Hurricane Irene blasted ashore at Cape Lookout, North Carolina on Saturday, a weakened but still massive category one storm on track to batter major US cities.

Sustained winds of 85 miles (140 kilometers) an hour lashed coastal areas as Irene made landfall near the southern end of a chain of barrier islands that ring the North Carolina coast, the National Hurricane Center said.

Trees were uprooted, highways closed and streets flooded, as powerful winds and heavy rain battered the coast and a local power company announced that 300,000 people were without electricity.

Cities along the east coast of the United States -- from Washington to New York to Boston -- braced for the impact, with hundreds of thousands of people ordered to evacuate low-lying areas.

The densely populated corridor, home to more than 65 million people, was under threat of flooding, storm surges, power outages and destruction that experts said could cost up to $12 billion.

"This is going to be a very serious storm, no matter what the track is, no matter how much it weakens. This is a life threatening storm to people here," New York Mayor Michael Bloomberg said.

Bloomberg has ordered an unprecedented mass evacuation and the rare closure of the city's extensive subway system, and US President Barack Obama has cut short his summer vacation and returned to Washington.

In North Carolina, Governor Bev Perdue said Irene had closed 10 major roads and breached two waste water treatment plants, although the damage assessments were preliminary.

"There are flash flood warnings throughout the east," she said. "We are concerned still about the storm surge after the rain begins to abate."

Homeland Security Secretary Janet Napolitano urged residents to abide by local evacuation orders, warning the "window of preparation is quickly closing."

"Even if you're not in an evacuation zone, please know this is a big storm that covers a lot of territory. Be prepared," she told CNN.

Bloomberg warned New Yorkers on Saturday not to be deceived by the storm's weakening, urging the 370,000 residents in low-lying areas under evacuation orders not to wait "until there are gale-force wind and rain to leave."

"Let's stop thinking this is something that we can play with. Staying behind is dangerous. Staying behind is foolish. And it's against the law," he said.

"The time to leave is right now. We just won't have the resources to get everyone in the evacuation zones out after the storm hits," he said.

New York's massive transit system was to begin to shut down midday Saturday, and all major New York area airports will close at noon (1600 GMT), officials said.

New York state meanwhile said major links into the city would be cut if winds exceeded 60 miles per hour, as predicted, and authorities called up 900 National Guard troops and 2,500 power workers to prepare for emergency repair work, the largest ever deployment.

Neighboring New Jersey on Thursday ordered 750,000 people out of the Cape May area.

The Miami-based NHC said Irene would likely remain a hurricane as it passed over or near the mid-Atlantic Saturday night.

Irene's approach stirred painful memories of Hurricane Katrina, which smashed into the Gulf Coast in 2005, stranding thousands of people in New Orleans and overwhelming poorly prepared local and federal authorities.

The popular North Carolina beach resort of Kill Devil Hills was a ghost town Saturday, as forecasters predicted up to 15 inches (38 centimeters) of rain in some places.

Irene will be accompanied by an "extremely dangerous" storm surge that could raise water levels by as much as 3.4 meters (11 feet), the NHC said.

Further north in Washington, residents have packed into supermarkets to stock up on emergency supplies, cleaning out shelves of bottled water and batteries.

Hurricanes are rare in the northeastern United States -- the last major hurricane to hit New York was Gloria in 1985.

The US military said up to 101,000 National Guard soldiers were available if needed and designated military bases in three states as staging areas.

Chuck Watson, research director at Kinetic Analysis, which does computer modeling of predicted storm damage, estimated $11 billion or $12 billion from Irene in a "worst-case scenario".

On New York's Rockaway Beach, Katie Richardson, 27, said on Friday that she and her friends -- all in town from Texas -- would make the most of their trip to the Big Apple, even if the city shuts down.

"We're going to ride this out with granola bars and Jameson," she vowed.