Houston’s recovery from Hurricane Harvey flooding will be a “multi-year project”, Texas Governor Greg Abbott has said.
“This is going to be a massive, massive clean-up process,” he told the ABC News programme Good Morning America.
President Donald Trump is to propose an initial $5.9bn (£4.56bn) for recovery efforts, but the Texas authorities say the state might need more than $125bn.
More than 40 people have died in the storm and its aftermath.
Recovery efforts in Houston are under way as the water recedes but search-and-rescue teams continued their work in the nearby city of Beaumont, Mr Abbott said on Friday.
Officials in Beaumont, a city of about 120,000 people near the Louisiana border, said Harvey’s flooding has cut off their drinking water supply.
Brad Penisson, a captain with the Beaumont fire and rescue department, said on Friday the city was setting up water distribution stations to ensure residents had clean drinking water.
Harvey made initial landfall as a Category 4 Hurricane in Texas last Friday, and has since 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 with rain.
An estimated 93,942 homes in Texas have been damaged or destroyed in the wake of Harvey, according to the Texas Division of Emergency Management. About 80% of Texans do not have flood insurance to cover the wreckage.
The storm has displaced thousands and about 32,000 people remain in shelters across the state, Mr Abbott said.
Visiting Texas, Vice-President Mike Pence on Thursday promised federal help to “rebuild bigger and better than ever before”.
The BBC’s Barbara Plett Usher in Houston says Congress is expected to act quickly on the request for initial funding when it reconvenes next week after its August recess.
But, she adds, that will be only the first tranche of money needed for the recovery.
Mr Pence said 311,000 people had registered for disaster assistance. It is not yet clear how quickly funds might reach victims.
Visiting the battered town of Rockport, Mr Pence paid tribute to the people of Texas: “The resilience of the people of Texas has been inspiring.”
The White House also said Mr Trump would donate $1m of his own money to the relief effort.
Dell Technologies CEO Michael Dell and his wife, Susan, have also pledged to donate $36m to launch a Rebuild Texas Fund with the aim of raising more than $100m for recovery efforts.
The couple, both Texas natives, said on Friday they plan to donate $18m immediately to launch the fund through their eponymous foundation.
Firefighters in Houston have been carrying out door-to-door searches for survivors and bodies in an operation that could take up to two weeks.
Hundreds of thousands of residents who were evacuated or chose to leave are being warned not to return home until they are told it is safe to do so.
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Officials in Harris County, where Houston is located, estimate 30,000 to 40,000 homes have been destroyed in area alone.
The US Federal Emergency Management Agency (Fema) said its teams had rescued more than 3,800 people, and more than 90,000 had already been approved for disaster assistance.
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“We need an army of Fema agents on the ground,” Mayor Sylvester Turner told CNN on Friday.
Fema also warned that residents were being targeted by scams. There are reports of criminals impersonating inspectors and immigration officials.
Others were receiving fraudulent calls about flood insurance claiming a premium must be paid or coverage would be lost.
Energy suppliers in southern Texas were forced to shut down refineries and close off pipelines, sending petrol prices higher across the US. Many have restarted operations, but it could take weeks before production is back to normal.
Residents returning to their homes are also facing challenges.
The Environmental Protection Agency is warning residents 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 remain without power.
One chemical plant in Crosby, near Houston, caught fire on Thursday, and more fires are expected in the coming days.
Chemicals stored at the flooded Arkema plant are no longer being refrigerated, making them combustible.
Residents have been evacuated from the plant in a 1.5-mile (2.5km) radius, and smoke was seen rising from the site on Thursday.
President Trump and his wife Melania are expected to return to Texas on Saturday.
The president visited the flood-hit state earlier in the week but limited his visit to Corpus Christi, which avoided the worst of the flooding, over fears his presence could divert resources from rescue efforts.
Storm Harvey has been downgraded to a tropical depression and is expected to dissipate over Ohio on Saturday evening.
Several inches of rainfall are expected in Tennessee and Kentucky over the next two days, and flood warnings remain in effect in parts of Arkansas, Mississippi, Tennessee, Kentucky, Texas, and Louisiana.