|New York Mayor Bloomberg has ordered unprecedented evacuations for a quarter of a million people [Al Jazeera]
At least five people have died in storm-related incidents as Hurricane Irene begins its destructive run along the US eastern seaboard.
On Saturday, one man died of a heart attack while boarding up his windows, another crashed his car into a tree, Tom Mather, a public affairs officer with the North Carolina emergency mangement office, said.
A third individual was killed after a vehicle drove into standing water and hit a tree, Mather said.
In Virginia, an 11-year-old boy died midday after a tree fell on an apartment complex in Newport News, Virginia, Bob Spieldenner, spokesman of the state's department of emergency management, said.
Another tree fell on a car and killed the passenger, Spieldenner said, adding there were no more details as of yet.
Hurricane Irene is lashing the southern coastal states with heavy winds, rain and surf while power cuts are reported for hundreds of thousands and New York City goes on lock down.
Irene made landfall on Saturday at around 11:30 GMT near Cape Lookout on the coast of eastern North Carolina carrying winds of 140km per hour, the Miami-based National Hurricane Center said.
"Irene is expected to remain near the threshold of Category One and Category Two strength," the center said in an advisory.
The Saffir-Simpson Hurricane Wind Scale uses five categories based on the hurricane's intensity at any given time.
The scale, originally developed by wind engineer Herb Saffir and meteorologist Bob Simpson, has been used for alerting the public about the possible impacts of various hurricanes.
A Category One hurricane displays sustained winds of 119-153km per hour, while a Category Five storm has winds greater than 249km per hour.
Although government forecasters have said the storm's intensity is likely to reduce, reclassifying it as a Category One Storm - the lowest grading, officials have warned of the storm's damaging effects.
Janet Napolitano, the US Homeland Security secretary, said a hurricane still remains a threat, regardless of its category.
"I would advise people not to focus that much on Category 1, 2 or 3 ... if you're in a hurricane, it's a big deal," Napolitano told a conference call.
"This remains a large and dangerous storm."
Phone and electricity down
More than 600,000 people are without electricity along the east coast as power plants cut their supply to ensure the units can keep running if the storm affects other parts of the grid.
The hurricane is on track to careen up the east coast late Saturday and Sunday, passing over or near Washington, New York and Boston, a densely populated urban corridor home to some 65 million people.
In the port and holiday city of Wilmington, North Carolina, thousands of people were without electricity as Irene's winds intensified.
The streets were empty before dawn and the air was filled with the smell and sound of pine trees cracking under the advancing storm.
Ed Rappaport, the deputy director of the National Hurricane Center, speaks to Al Jazeera from Miami about the impending storm
In summer weather, the area sees hundreds of thousands of residents and vacationers, but most have evacuated from Irene's path.
Supermarkets and hardware stores, meanwhile, were inundated with people stocking up on food, water, flashlights, batteries, generators and other supplies.
"Our number of customers has tripled in the last day or two as people actually said 'Wow, this thing is going to happen'," said Jack Gurnon, owner of a hardware store in the northeastern city of Boston.
Airlines cancelled nearly 7,000 flights over the weekend and all three New York area airports were due to close to incoming flights at noon (1600 GMT) on Saturday.
Tens of thousands of people on the East Coast were on the move on Saturday, fleeing their homes and vacation spots ahead of the massive Irene.
Mass evacuations ordered
Airports, transit systems and scores of businesses were shut down.
Michael Bloomberg, the New York mayor, ordered an unprecedented mass evacuation and the closure of the subway system while Barack Obama, the US president, cut short his summer vacation and returned to Washington.
"We can't depend on mother nature being so kind. We've to prepare for the worst and hope for the best," Bloomberg said.
More than 370,000 people have been ordered out of low-lying parts of the city by 5 PM (local) Saturday, 1,400 of which are staying in shelters, the mayor said.
He added it was not immediately clear how many people are defying the evacuation order.
Obama said the storm could be "extremely dangerous and costly" for a nation that recalls the destruction in 2005 from Hurricane Katrina, which swamped New Orleans, killed up to 1,800 people and caused $80bn in damage.
Irene, the first hurricane of the 2011 Atlantic season, caused as much as $1.1bn in insured losses in the
Caribbean, catastrophe modeling company AIR Worldwide said.
Losses are expected along the US east coast from high winds, heavy seas, flooding and fallen trees. Irene is the first hurricane to hit the US mainland since Ike pounded Texas in 2008.
Leon Panetta, the US defence secretary, said the military stood ready to help, with more than 100,000 National Guard forces available if needed in eastern states.
Source: Al Jazeera and agencies