More than two million people have been ordered to leave their homes ahead of the massive category one storm.
In New York City, a quarter of a million people living in low-lying areas have been told to leave in an unprecedented mandatory evacuation.
The city mayor warned it was “foolish” and “dangerous” to ignore the order.
New York State is one of seven states from North Carolina to Connecticut have declared emergencies.
US President Barack Obama has warned Irene could be “a historic hurricane”.
He has urged people in the projected path of Hurricane Irene – the first hurricane of the Atlantic season – to take precautions.
“Don’t wait, don’t delay. All of us have to take this storm seriously,” he said on Friday, before cutting short his holiday in Martha’s Vineyard on the Massachusetts coast, to head back to Washington