US President Barack Obama has declared a "major disaster" in North Carolina and New York state, in the wake of Tropical Storm Irene.
Mr Obama's move allows the two states to tap extra funds for relief efforts.
Swollen rivers along the north-eastern seaboard have begun receding after they caused extensive flooding and prompted emergency rescues in states such as New Jersey.
The storm has been blamed for at least 45 deaths in 13 states.
Irene barrelled along the east coast over the weekend, delivering hurricane force winds in North Carolina and torrential rains in New York, New Jersey, Connecticut and Vermont, which forced rivers to swell and prompted extensive flooding.
Nuclear reactors affected
The storm drenched the east coast with up to 15in (38cm) of rain at the weekend, setting river level records in 10 states, the US Geological Survey said.
At least 1.7 million homes and businesses in the affected areas are still without power.
Two out of three nuclear reactors in a southern New Jersey county have moved to reduce power because debris from Hurricane Irene was blocking cooling-water intakes.
Mr Obama earlier signed an emergency declaration for Vermont following the storm, which caused damage estimated at more than $10bn (£6.5bn) and forced a shutdown of New York City.
About two million people on the US east coast are still without power after Irene wreaked havoc on both small towns and major cities, some far inland.
Rescue operations continued on Wednesday in the north-east, clearing roads and delivering supplies to stranded towns - where mud-coloured floodwaters had earlier washed homes and businesses away from their foundations.
President Obama will view the damage from Irene on Sunday in Paterson, the third-largest city in the state of New Jersey.
Emergency teams in Paterson have been rescuing residents after the Passaic river reached 13ft (4m) above its banks late on Tuesday - its highest level since 1903.
The Passaic was receding on Wednesday, said James Furtak, acting emergency management director of Bergen County.
In Connecticut, the National Weather Service has warned of moderate to major flooding on the Connecticut River, which peaked in the city of Middletown at 15.4ft on Wednesday morning.
Irene swept up the heavily populated eastern seaboard after making landfall as a category one hurricane in North Carolina.
By the time it reached New York, it had been downgraded from a hurricane to a tropical storm.
Nonetheless, the New York subway system was closed for the first time in its history, while 370,000 people living in low-lying areas were ordered to leave their homes.
The governors of New York, New Jersey and Connecticut requested disaster declarations on Tuesday.
In a letter to the president, Governor Andrew Cuomo of New York said that he had seen "hundreds of private homes destroyed or with major damage and an enormous amount of public infrastructure damage".
These sentiments were echoed in a letter to the president by Governor Chris Christie of New Jersey, whose state has not yet been designated a recipient of disaster funds.
Homeland Security Secretary Janet Napolitano visited that state on Wednesday to survey the damage.
In Vermont on Tuesday night, more than 200 roads were blocked or had been washed away, hampering rescue efforts to as many as 13 towns.
Relief crews have now reached all of the towns, although most are passable only by emergency vehicles.
National Guard troops have brought in food, water and other emergency supplies to cut-off areas in the rural, mountainous state.