About 100,000 homes have been affected by Storm Harvey and the flooding it brought to parts of the southern US, a White House aide has said.
Homeland Security adviser Tom Bossert said the White House would ask Congress for emergency funding to help those affected, some of whom are uninsured.
Meanwhile, US President Donald Trump is said to have pledged $1m (£770,000) of his own money to the relief effort.
At least 33 people have died since the storm hit Texas last Saturday. A number of deaths are still being investigated.
Firefighters have begun a door-to-door search for survivors and bodies in an operation that could take up to two weeks.
Oil refineries and pipelines have been shut down, and a fire broke out at a chemical plant near Houston.
More fires and possibly explosions are expected at the Arkema liquid organic peroxide plant, and the area around it has been evacuated up to a radius of 1.5 miles (2.4km).
A hospital in Beaumont, east of Houston, was forced to evacuate patients on Thursday after the local water supply shut down. Military Black Hawk helicopters were used to airlift intensive care patients.
Storm Harvey has now been downgraded to a tropical depression, but heavy rainfall is expected from Louisiana to Kentucky over the next three days and flood warnings remain in effect for south-east Texas and parts of south-west Louisiana.
At a news conference on Wednesday, Texas Governor Greg Abbott said the state could need more than $125bn from the federal government to help it recover.
Bossert told reporters that the administration would “put together a responsible supplemental request for Congress” for funds. He did not give a figure but said Governor Abbott had made a fair estimate of the cost.
The request would be followed by a second one later when recovery needs were clearer, he said.
Parts of Texas have been hit by more than 50in of rainfall since Hurricane Harvey landed on 25 August, setting new records before it was downgraded to a tropical storm and, late on Wednesday, to a tropical depression.