With winds of 90 miles per hour, Irene weakened slightly to a Category 1 hurricane on the five-step Saffir-Simpson scale by early Saturday but forecasters warned that it remained a large and dangerous storm.
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.
Airlines canceled nearly 7,000 flights over the weekend and all three New York area airports were due to close to incoming flights at noon Saturday.
President Barack 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 $80 billion in damage.