WASHINGTON - US President Barack Obama late Thursday declared an "emergency" in flood-hit New York state.

"The president today declared an emergency exists in the State of New York and ordered federal aid to supplement state and local response efforts due to the emergency conditions resulting from the remnants of Tropical Storm Lee beginning on September 7, 2011, and continuing," the White House said in a statement.

Remnants of Lee swamped the already-soggy US east coast since Wednesday, leaving at least five people dead and spurring flash floods.

Several counties in New York, New Jersey, Pennsylvania, Connecticut, Maryland and Virginia are under flash flood warning, according to the National Weather Service.

In hard-hit Binghamton, New York state, the Susquehanna River spilled over its banks and flowed into city streets. Approximately 20,000 people there were ordered to leave their homes.

"We are on the verge of a crisis and federal assistance is urgently needed to help protect New Yorkers," New York Governor Andrew Cuomo's office said in a statement. "Communities in eastern and central New York, from the southern Adirondacks to the Pennsylvania border, who were struggling to clean up and rebuild after Irene, are facing another onslaught of devastation."

In Pennsylvania, some 100,000 people were ordered to evacuate Thursday, as the Susquehanna River was expected to crest there early Friday to almost the same height as the levee system.

Some portions of the US east coast are still recovering from damages caused by Hurricane Irene. The powerful storm slammed the area late August with high wind, torrential rains, tidal waves and flooding, causing massive destruction to roads and houses while leaving 7 million customers without power.