TROPICAL storm-force winds from Hurricane Irene began lashing the US East Coast with rain yesterday with the potential to cause billions of dollars in damage along a densely populated arc that included Washington, Baltimore, Philadelphia, New York and Boston. At least 65 million people could be affected.

A hurricane warning was in effect from North Carolina all the way to Massachusetts - including for New York City, where more than a quarter-million people were ordered to evacuate ahead of Irene's approach. It was the first hurricane warning issued for New York City in more than two decades.

Officials declared emergencies, called up hundreds of National Guard troops, shut down public transit systems and begged hundreds of thousands of people to obey evacuation orders. Airlines canceled more than 2,000 weekend flights.

The National Hurricane Center said the storm is unlikely to get any stronger and may weaken slightly before reaching land. It said Irene could weaken to a tropical storm before reaching the northern region of New England, but that even below hurricane strength it would be a powerful and potentially destructive storm.

As the storm's outermost bands of wind and rain began to lash islands off the coast of the southern state of North Carolina, authorities in points farther north begged people to get out of harm's way. The hurricane lost some strength but still packed 160 kph winds, and officials in the Northeast, not used to tropical weather, feared it could wreak devastation.

Speaking from Martha's Vineyard Island where he is vacationing, President Barack Obama said all indications point to the storm being a historic hurricane.

"Don't wait. Don't delay," said Obama, who decided to cut short his summer vacation by a day and return to Washington. "I cannot stress this highly enough: If you are in the projected path of this hurricane, you have to take precautions now."

Senior hurricane specialist Richard Pasch of the National Hurricane Center said there were signs that the hurricane may have weakened slightly, but strong winds continued to extend 160 kilometers from its center.

The latest forecasts showed Irene crashing into the North Carolina coastline today, then churning up the Eastern Seaboard and drenching areas from Virginia to New York City before a weakened storm reaches New England.

Rain and tropical storm-force winds of at least 63 kph already were pelting North and South Carolina as Irene trudged north, snapping power lines and flooding streets. Officials warned of dangerous rip currents as Irene roiled the surf. Thousands already were without power. In Charleston, South Carolina, several people had to be rescued after a tree fell on their car, trapping them.

The hurricane forced the president to wrap up his vacation a day early to return to Washington last night instead of this afternoon.

Irene's wrath in the Caribbean, including Puerto Rico, the Dominican Republic and the Bahamas, gave a preview of what might be coming to the US: Power outages, dangerous floods and high winds that caused millions of dollars in damage.

The US East Coast, home to some of the country's most densely populated cities and costliest waterfront real estate, was expected to suffer a multibillion-dollar disaster, experts forecast.

In the Carolinas, swells and waves up to 3 meters were reported along the Outer Banks and thousands had already lost power as the fringes of the storm began raking the shore.

In addition to widespread wind and water damage, Irene could also push crude oil prices higher if it disrupts refineries in Delaware, New Jersey, Pennsylvania and Virginia, which produce nearly 8 percent of US gasoline and diesel fuel.

The center of the storm was still about 427 kilometers south-southwest of Cape Hatteras, North Carolina, and moving to the north at 22 kph. Forecasters warned wind-whipped water could create a dangerous storm surge, with levels along the state's Albemarle and Pamlico sounds rising as much as 3.35 meters.

In Washington, Irene dashed hopes of dedicating a 10-meter sculpture to Martin Luther King Jr. tomorrow on the National Mall. While a direct strike on the nation's capital appeared slim, organizers said the forecasts of wind and heavy rain made it too dangerous to summon a throng they expected to number up to 250,000.

Hundreds of thousands of New Yorkers were told on Thursday to pack a bag and be prepared to move elsewhere. Gov. Andrew Cuomo said public transportation in New York City would shut down around noon (1700 GMT) today, and major bridges also could shut down if conditions become too windy.

The nation's biggest city has not seen a hurricane in decades, and a hurricane warning hasn't been issued there since Hurricane Gloria hit in 1985 as a Category 2 storm, said Ashley Sears, a meteorologist with the National Weather Service.

Even if the winds aren't strong enough to damage buildings in a metropolis made largely of brick, concrete and steel, a lot of New York's subways and other infrastructure are underground, making them subject to flooding.

New York's two airports are close to the water and could be inundated, as could densely packed neighborhoods, if the storm pushes ocean water into the city's waterways, officials said.

The five main New York City-area airports will be closed to arriving passenger flights beginning at noon (1700 GMT) today, aviation officials said.

The Port Authority of New York and New Jersey, which operates the airports and area bridges and tunnels, said yesterday that many weekend departures already had been canceled in anticipation of the hurricane.

Hundreds of flights could be affected, Port Authority spokesman Steve Coleman said. The airports handle about 3,000 flights each day on average during the week, fewer on weekends, he said.

In 2008, the city had a brush with Tropical Storm Hanna, which dumped 8 centimeters of rain on Manhattan.

In the last 200 years, New York has seen only a few significant hurricanes. In September 1821, a hurricane raised tides by 4 meters in an hour and flooded all of Manhattan south of Canal Street, the southernmost tip of the city. The area now includes Wall Street and the World Trade Center memorial.

An infamous 1938 storm dubbed the Long Island Express came ashore about 120 kilometers east of the city and then hit New England, killing 700 people and leaving 63,000 homeless.

The first US injuries from Irene appeared to be in South Florida near West Palm Beach, where eight people were washed off a jetty on Thursday by a large wave churned up by the storm.