More than a million people have been displaced by the disaster in Texas
Donald Trump has asked Congress for an initial $7.85bn (€6.6bn) in disaster relief in the wake of Hurricane Harvey.
The request comes ahead of the US President's second visit to the storm-ravaged region later, when he will visit Houston, Texas, and Lake Charles, Louisiana.
White House budget director Mick Mulvaney told Congress: "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."
White House homeland security adviser Tom Bossert said further funding requests would come in stages as more became known about the impact of the storm.
Harvey was the most powerful hurricane to hit Texas in half a century, and went on to dump unprecedented amounts of rain and wreak devastation across more than 300 miles (480 km) of the state's coast.
More than 1 million people have been displaced and officials said at least 46 are feared dead.
The US Coast Guard said it had rescued at least 3,000 people from floodwaters in the last 48 hours, while more than 150,000 homes have been flooded in one county of Texas alone.
More than 46,000 Texans have seen their properties badly damaged with 9,000 homes destroyed.
As many as 20,000 homes in western Houston could also continue to be flooded for up to 15 days as authorities told residents to evacuate as they planned a release from two reservoirs to protect the centre of the city.
Two trailers of highly unstable compounds also blew up at a chemical plant east of Houston. An executive said further blasts were likely in six other trucks storing the same chemicals.
Meanwhile, Texas Governor Greg Abbott reassured residents the state's petrol pumps would not run dry thanks to the reversal of a pipeline that usually supplies Oklahoma, despite widespread reports of fuel shortages caused by panic-buying.
Mr Abbott warned it could take years for Texas to "dig out from this catastrophe" while, despite claiming the state is "healing fast", Mr Trump added there is "still so much to do".
The President thanked his wife Melania, who joined him on his Tuesday trip to Texas, for being "so dedicated" to relief efforts as he revealed the First Lady has been "very much affected" by the disaster.
Flanked by the leaders of the Salvation Army, American Red Cross and Southern Baptist Disaster Relief in the Oval Office, the President said: "I want to thank my wife Melania, the First Lady, she's been so involved in this and helping so much."
Invited by the President to say a few words herself, Mrs Trump said: "It's great to be here with amazing people and I want to thank all the volunteers all across the country that came to help in Texas. A fantastic job.
"We are going tomorrow to visit them and I just want to tell them to be strong and everything will be OK."
Mr Trump, who has declared Sunday a national day of prayer for the disaster, remarked: "I didn't tell her I was going to do that. And she did a great job.
"She really has, she's been so dedicated to this, this has very much affected her what's happened in Texas and neighbouring states, frankly.
"So I want to thank you, first lady."