US President Donald Trump has asked Congress for $7.8bn (£6bn) as an initial payment to help with recovery efforts following flooding in Texas and Louisiana.
Officials say there will be further requests for funds when the full impact of Hurricane Harvey becomes known.
Some residents have been allowed to return to their homes but flood waters are still rising in other areas.
Mr Trump is to visit Texas for a second time on Saturday.
The hurricane made landfall in the state a week ago, causing devastating floods.
It has been blamed for the deaths of at least 47 people and about 43,000 are currently housed in shelters.
In a letter to House of Representatives Speaker Paul Ryan, White House budget director Mick Mulvaney warned that failure to raise the US debt ceiling could hinder recovery efforts.
The debt ceiling is a cap on the total amount the US government can borrow. Only Congress can raise that limit.
“This request is a down-payment on the president’s commitment to help affected states recover from the storm, and future requests will address longer-term rebuilding needs,” Mr Mulvaney said.
Governor of Texas Greg Abbott has said the state may need more than $125bn in aid.
Mr Mulvaney said almost half a million households had registered for support for rental assistance and for essential home repairs.
He called on Congress to act “expeditiously to ensure that the debt ceiling does not affect these critical response and recovery efforts”. A vote on the emergency request is expected next week.
It is believed that about 80% of Texans do not have flood insurance to cover the wreckage.
Harvey dumped an estimated 20 trillion gallons of rain on the Houston area. It was later downgraded to a tropical storm but continued to batter Texas and parts of neighbouring Louisiana.
Governor Abbott warned on Friday that the recovery programme would be a “multi-year project”.
“This is going to be a massive, massive clean-up process,” he told ABC News.
As the water recedes in Houston a huge clean-up operation is under way. Firefighters have been carrying out door-to-door searches in an operation that could take up to two weeks.
Mr Abbott warned that in some parts of the state, rivers were still rising and flooding “poses an ongoing threat”.
Search-and-rescue teams have continued work in Beaumont, a city of about 120,000 people near the Louisiana border, where flooding has cut off the drinking water supply.
The Environmental Protection Agency has warned that floodwater can contain bacteria and other contaminants from overflowing sewers. It said the biggest threat to public health was access to safe drinking water.
Thousands of homes and businesses remain without power.
President Trump and his wife Melania visited Texas earlier in the week but stayed clear of the disaster zone, saying they did not want to divert resources from rescue efforts.
However, Mr Trump was criticised for not meeting victims of the flooding and for focusing largely on the logistics of the government response.
The White House said he would visit Houston on Saturday to meet flood survivors and volunteers and would then travel to Lake Charles, Louisiana.
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