U.S. President Barack Obama has cautioned Americans that the impact of Hurricane Irene “will be felt for some time.”

Mr. Obama said Sunday, “This is not over yet” and that the public is still at risk of flooding and power outages. He said it could take days or weeks for a recovery effort to end on the U.S. east coast.

The president has declared an emergency for most of the states hit by Irene, including North Carolina, Virginia and New York, in order to make federal resources available to support response efforts.

The National Hurricane Center says Irene is no longer a hurricane. The storm still has winds of 85 kilometers per hour, and will move into Canada early Monday, where 20 centimeters of rain could fall across Nova Scotia and New Brunswick.

The storm killed at least 18 people and paralyzed ground and air traffic in its journey up the eastern U.S. coast.

Major airports serving New York are expected to re-open early Monday. New York's subway system will be available for commuters to return to work Monday morning.

More than 4 million homes and businesses along the east coast have lost power.

New Jersey Governor Chris Christie has predicted record-level flooding for parts of his coastal state, and Pennsylvania Governor Tom Corbett has warned that rivers in the affected areas of his state may not crest until Tuesday or Wednesday.

Irene blasted ashore in North Carolina early Saturday, flooding streets and toppling trees with winds of 140 kilometer per hour. The storm later moved into the Washington area, which was hit with strong winds, heavy rain, localized flooding and falling trees.