HOUSTON (REUTERS) - Rescuers searched painstakingly through flooded neighbourhoods across south-eastern Texas on Friday (Sept 1) for people stranded by Hurricane Harvey's deluge as President Donald Trump asked Congress for US$7.85 billion (S$10.7 billion) in federal disaster relief.

The storm, one of the costliest to hit the United States, has displaced more than one million people, with 50 feared dead from flooding that paralysed Houston, swelled river levels to record highs and knocked out the drinking water supply in Beaumont, Texas, a city of 120,000 people.

The Trump administration in a letter to Congress asked for a US$7.85 billion appropriation for response and initial recovery efforts. White House homeland security adviser Tom Bossert told reporters on Thursday that aid funding requests would come in stages as more became known about the impact of the storm.

Trump plans a second visit to the region on Saturday.

Though the sun was out in Houston on Friday and water levels down in many areas, Mayor Sylvester Turner called for voluntary evacuations on the city's west side. He said already-flooded neighbourhoods there may be in greater danger as the Army Corps of Engineers continues to release water into the adjacent Buffalo Bayou to prevent dam and levee failures.

About 130km to the east, the Neches River, which flows into Beaumont and nearby Port Arthur, was forecast to crest on Friday.

"There still remain areas that are deadly dangerous," Texas Governor Greg Abbott told reporters. "The Neches River continues to rise. It is about 7 ft (2.1m) above the record and it will continue to remain at or be near that high for about the next week. This flooding poses an ongoing threat."

Rescue officials were still working to determine the scope of flooding, said Rodney Smith, deputy chief of the Cedar Hill, Texas, Fire Department.

The storm's impacts played out in ways large and small, a full week after Hurricane Harvey slammed into the Texas coast Friday night as a Category 4 storm.

At the Hollywood Community Cemetery in Orange, floodwaters had caused three coffins to pop out of their concrete vaults. One belonged to Dewey Mosby, who died in 2003 at the age of 82.

"He won't stay put," said Ron Kendall, 63, who helps maintain the cemetery and said he knew Mosby well in life. Kendall had helped direct Mosby's coffin back to its resting place after the 2008 floods from Hurricane Ike and again during floods in 2016.

"Everybody knows where Mr Mosby goes now because he always comes up," Kendall said.

BURNING CHEMICALS

At chemical maker Arkema SA, a fire started on Thursday in a truck storing chemicals at a flooded plant east of Houston had burned itself out by Friday. But more blasts were likely in eight other trucks storing the same chemicals. .

Meanwhile a new storm, Irma, had strengthened on Friday into a Category 3 on the five-step Saffir-Simpson scale. It remained hundreds of miles from land but was forecast to possibly hit Puerto Rico, the Dominican Republic and Haiti by the middle of next week.

Harvey was the most powerful hurricane to hit Texas in half a century, and went on to dump unprecedented amounts of rain and leave devastation across more than 480km of the state's coast.

A list of the dead put out by Harris County officials painted a grim picture of the storm's brutality, describing bodies found floating face down in floodwaters, lying in ditches or across fences. Many were unidentified.

The storm shut about a fourth of US refinery capacity, much of which is clustered along the Gulf Coast, and caused gasoline prices to spike to a two-year high ahead of the long Labour Day holiday weekend.

The national average for a gallon of regular gasoline has risen 17 cents since the storm hit, hitting US$2.519 as of Friday morning, according to motorists group AAA.

Supply concerns prompted the US Energy Department to authorise the release of up to 4.5 million barrels of oil from the Strategic Petroleum Reserve.

Several East Coast refineries have run out of gasoline, raising fears that travelers will face fuel shortages during the three-day holiday.

In major Texas cities including Dallas, there were long lines at gas stations. Abbott said the state was taking steps to ensure adequate supplies, adding: "Don't worry. We will not run out of gasoline."

Harvey came on the 12th anniversary of Hurricane Katrina, which killed about 1,800 around New Orleans. Then-US President George W. Bush's administration was roundly criticised for its botched early response to the storm.

"The people of Texas and Louisiana were hit very hard by a historic flood and their response taught us all a lesson, a very, very powerful lesson," Trump said. "There was an outbreak of compassion only ... and it really inspired us as a nation."

Some 440,000 Texans have already applied for federal financial disaster assistance, and some US$79 million has been approved so far, Abbott said.

Moody's Analytics estimated the economic cost from Harvey for southeastern Texas at US$51 billion to US$75 billion.