One of the worst hit areas is eastern Pennsylvania where county officials have ordered the evacuation of up to 200,000 people from low-lying areas around the Susquehanna River.
The order covered the city of Wilkes-Barre which is protected by a system of dykes similar to the one around New Orleans that was breached by Hurricane Katrina last year with devastating consquences.
"We were afraid of a New Orleans-type situation where we just couldn't get people out," Pennsylvania Governor Ed Rendell said, explaining the evacuation move.
A state of emergency was declared in 46 Pennsylvania counties and Governor Rendell said helicopters had already been brought in to fly search and rescue missions, plucking stranded residents from their rooftops.
"The next 12 to 14 hours will tell whether this is a full-scale disaster," the governor told CNN.
Leaking dam
The fatalities from the regional floods included three dead in Maryland, three in New York state and one in Pennsylvania.
In Maryland, two men and one woman drowned after flood waters swept them from a stalled pickup truck in Frederick County while another person died "as a result of flooding" in Wayne County,
Pennsylvania.
New York state police confirmed three storm-related fatalities, including two truck drivers whose vehicles crashed into a sinkhole on Interstate 88 in Delaware County. A man was confirmed dead in nearby Chenango County after his car was swept away by floodwaters.
A leaking dam, swollen to near-bursting after days of torrential rain, forced 2,300 people to evacuate their homes in Montgomery County, Maryland, outside Washington.
As Maryland's Lake Needwood swelled to eight meters above its normal level, police went door to door to order people from their homes around the lake.
Bill Delaney, assistant public information officer for the Montgomery
County Fire and Rescue Service, said it was not yet clear when residents could return.
A stationary storm front has dumped up to 25 centimeters of rain in the Washington area and elsewhere along the US East Coast over the last four days.
Washington Mayor Anthony Williams declared a state of emergency for the capital, enabling him to request assistance from the National Guard, after flooding caused extensive damage and disruption.