Rain and tropical storm-force winds of at least 39 mph (63 kph) already were pelting the Carolinas 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, S.C., several people had to be rescued after a tree fell on their car, trapping them.
For hundreds of miles, people in the storm's path either fled inland or stocked up on supplies to ride it out. Irene had the potential to cause billions of dollars in damage and affect some 65 million people in cities including Washington, Baltimore, Philadelphia, New York and beyond.
Officials along the entire Eastern Seaboard 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 ahead of the storm, which federal officials said is likely to affect more people than many others before it.
President Barack Obama said all indications point to the storm being historic.
"I cannot stress this highly enough. If you are in the projected path of this hurricane, you have to take precautions now," said Obama, who was wrapping up his Martha's Vineyard vacation a day early and heading back to the White House on Friday.
Irene's wrath in the Caribbean, including Puerto Rico, the Dominican Republic and the Bahamas, gave a preview of what is expected in the U.S.: Power outages, dangerous floods and high winds that caused millions of dollars in damage.
Hurricane warnings remained in effect from North Carolina to New Jersey. Hurricane watches were in effect even farther north and included Long Island, Martha's Vineyard and Nantucket, Mass.
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 U.S. gasoline and diesel fuel.
By Friday afternoon, Irene had weakened slightly but remained a Category 2 storm with maximum sustained winds near 100 mph (161 kph). Little change in strength was expected by the time Irene reaches North Carolina on Saturday, but forecasters at the National Hurricane Center warned it would be a large and dangerous storm nonetheless.
In North Carolina, traffic was steady Friday as people fled the Outer Banks and beach towns. Tourists had been ordered to leave the barrier islands, though local officials estimated Friday that about half the residents on two of the islands have ignored evacuation orders.
In Nags Head, police officer Edward Mann cruised the streets in search of cars in driveways — a telltale sign they planned to stay behind. He warned those that authorities wouldn't be able to help holdouts in hurricane-force winds, and that electricity and water could be out for days.
Some tell Mann they're staying because they feel safe or because the storm won't be as bad as predicted. Mann, 25, said some have told him they've ridden out more storms than years he's been alive.
Bucky Domanski, 71, was among those who told Mann he wasn't leaving. The officer handed the retired salesman a piece of paper warning of the perils of staying behind. Domanski said he understood.
"I could be wrong, but everything meteorologists have predicted never pans out," Domanski said. "I don't know, maybe I've been lulled to sleep. But my gut tells me it's not going to be as bad as predicted. I hope I'm right."
Speaking Friday on CBS' "The Early Show," North Carolina Gov. Beverly Perdue said state troopers, the Red Cross and the National Guard were in place to deal with the storm's aftermath, which she said could affect some 3.5 million people.
North Carolina was just first in line along the Eastern Seaboard — home to some of the nation's priciest real estate.
Besides major cities, sprawling suburbs, ports, airports, highways, cropland and mile after mile of built-up beachfront neighborhoods are in harm's way. In several spots along the coast, hospitals and nursing homes worked to move patients and residents away from what could be the strongest hurricane to hit the East Coast in seven years.
The center of the storm was still about 300 miles (483 kilometers) south-southwest of Cape Hatteras, N.C., and moving to the north at 14 mph (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 11 feet.
The latest forecasts showed Irene crashing into the North Carolina coastline Saturday, then churning up the Eastern Seaboard and drenching areas from Virginia to New York City before a weakened storm reaches New England.
In Washington, Irene dashed hopes of dedicating a 30-foot sculpture to Martin Luther King Jr. on Sunday on the National Mall. While a direct strike on the nation's capital appeared slim, organizers said forecasts of wind and heavy rain made it too dangerous to summon a throng they expected to number up to 250,000.
The city of Alexandria, Va., just outside Washington ran out of the free sandbags provided to residents at three distribution centers, though officials hoped to have more later Friday.
In nearby McLean, shoppers crowded into grocery and hardware stores to stock up on food, flashlights, gas cans, drills, coolers and wet vacs. McLean Hardware employee John Crawford said the last-minute shopping didn't compare to the rush before the massive snowstorm that hit the D.C. area in February 2010.
"This is not that bad at all," he said.
In the Sandbridge section of Virginia Beach, Va., rental companies raced to evacuate guests and board up rental homes.
John Landbeck of Aberdeen, Md. spent Friday morning packing up the vacation home he was renting and pulling his fishing boat out of the water. He planned to ride out the storm at a hotel in Chesapeake and return to his rental for another two weeks once the storm passed. He said he'd stay out of harm's way but was taking things in stride.
"Hopefully we won't have any earthquakes, no more hurricanes, no more floods. But It's been fun. For me, life is an adventure. Whatever comes, we take it," he said.
More than a quarter-million New Yorkers were ordered to evacuate the city's low-lying coastal areas Friday. The transit system in the city — where few people have a car — would shut down around noon Saturday, the first time the entire system has ever been halted. A hurricane warning has not been issued for the nation's biggest city 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.
Philadelphia officials also planned to shut down the city's transit system early Sunday morning.
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.
In the last 200 years, New York has seen only a few significant hurricanes, and New England is unaccustomed to direct hits. In 1938, a storm dubbed the Long Island Express came ashore about 75 miles east of the city and then hit New England, killing 700 people and leaving 63,000 homeless.
Across the Northeast, Irene threatened to flood many miles of land that are already saturated from heavy rain. Parts of Rhode Island are still recovering from devastating 2010 spring floods.
Back in North Carolina, officials also were preparing for what might happen to those who don't evacuate. Richard Marlin, the fire chief in Frisco, said he ordered 75 extra body bags for a town that normally keeps 10 on hand.
"I anticipate we're going to have people floating on the streets, and I don't want to leave them lying there," Marlin said. If the storm maintains its current track, "the Coast Guard will either be pulling people off their roofs like in Katrina or we'll be scraping them out of their yards."
Associated Press writers Michael Biesecker in Raleigh, N.C.; Jennifer Peltz in New York; Seth Borenstein in Washington; Wayne Parry, Geoff Mulvihill and Bruce Shipkowski in New Jersey; Brock Vergakis in Virginia; Randall Chase in Ocean City, Md.; Harry Weber in Miami; Martha Waggoner in North Carolina; David Sharp in Portland, Maine; and Bruce Smith in Pawleys Island, S.C., contributed to this story.