US President Barack Obama officially declared the floods caused by Tropical Storm Irene in North Carolina and New York a major disaster.
The move allows the two states to tap extra federal funds for relief efforts.
President Obama earlier signed emergency declarations for other states including Vermont.
About 40 people in the US were killed by the storm, which also caused damage estimated at more than $10bn and forced a shutdown of New York City.
Millions of people on the US east coast are still without power after Irene, which made landfall in the US on Saturday.
Rescue operations continued into the night on Tuesday, clearing roads and delivering supplies to stranded towns.
Some areas are still at risk of flooding as some rivers are expected to crest on Wednesday.
Irene swept up the heavily populated eastern seaboard from 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 because of a natural disaster, while 370,000 people living in low-lying areas were ordered to leave their homes.
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 by Governor Chris Christie of New Jersey, whose state has not yet been designated a disaster funds recipient.
Mr Christie wrote to the president saying that "immediate federal assistance is needed now to give New Jersey's residents a helping hand at an emotionally and financially devastating time."
Homeland Security Secretary Janet Napolitano will visit the state on Wednesday to survey the damage.
One of Many
President Obama had already declared a major disaster in the US territory of Puerto Rico, which felt the early force of Irene as it moved through the Caribbean.
Earlier, emergency declarations were issued for states along the eastern seaboard from North Carolina through the Washington DC area and onwards to New York and the New England states.
A disaster declaration is granted by the president upon request from a state when the cost of damage is so great that the state needs additional funding for relief operations.
New Jersey and upstate New York have been badly affected as the rain from Irene swells rivers and flows south
In Vermont on Tuesday night, more than 200 roads were blocked or have been washed away, hampering rescue efforts to as many as 13 towns.
Irene had been expected to bring the most havoc to coastal areas, but some of its worst destruction took place far inland.