(Updates death toll to 50, new evacuations ordered)
ORANGE, Texas/HOUSTON, Sept 1 (Reuters) - Rescuers searched painstakingly through flooded sections of southeastern Texas on Friday for people stranded by Hurricane Harvey's deluge as Houston's mayor warned residents of the city's west their homes may not dry out for weeks.
The storm, one of the costliest to hit the United States, has displaced more than 1 million people, with up to 50 feared dead from flooding that paralyzed Houston, swelled river levels to record highs and knocked out the drinking water supply in Beaumont, Texas, a city of some 120,000 people.
Though the sun was out in Houston on Friday and water levels have dropped in many areas, Mayor Sylvester Turner called for voluntary evacuations on the city's west side. He said neighborhoods there may remain flooded as the Army Corps of Engineers continues to release water into the adjacent Buffalo Bayou to prevent dam and levee failures.
About 80 miles (130 km) 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 feet (2.1 meters) 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.
Sam Dougharty, 36, was shocked when water began to flow in beneath his front door during Harvey's rains in Orange, Texas, earlier this week.
"We never had water here," he said. "This is family land. My aunt's owned it for 40 years and never had water here."
As the water rose, Dougharty, his wife, Lacey, and their three children fled to a relatives' house in Louisiana.
They returned on Friday to find their yard transformed into a thigh-high lake, the house smelling like raw sewage. A calf and a heifer from their herd of 15 were dead. The chickens were sagging on the top two roosts of their coop, staring at the water quietly.
Chemical maker Arkema SA said a fire started on Thursday in a truck storing chemicals at a flooded plant east of Houston had burned itself out by Friday, but that more blasts were likely in eight other trucks storing the same chemicals.
STORM IRMA BUILDS IN THE ATLANTIC
With three months remaining in the official Atlantic hurricane season, a new storm, Irma, had strengthened on Friday into a Category 3 storm on the five-step Saffir-Simpson scale, on Friday. It remained hundreds of miles from land but was forecast to possibly hit Puerto Rico, the Dominican Republic and neighboring Haiti by the middle of next week.
Harvey roared ashore a week ago as a Category 4 storm, the most powerful hurricane to hit Texas in half a century. It dumped unprecedented amounts of rain and left devastation across more than 300 miles (480 km) of the state's coast.
The storm shut about a fourth of U.S. 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 Labor Day holiday weekend.
The national average for a gallon of regular gasoline has risen 17 cents since the storm hit, hitting $2.519 as of Friday morning, according to motorists group AAA.
Supply concerns prompted the U.S. Energy Department to authorize 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-U.S. President George W. Bush's administration was roundly criticized for its botched early response to the storm.
Signaling that he did not want to be seen as repeating those mistakes, President Donald Trump plans a second visit to the region on Saturday.
"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 $79 million has been approved so far, Abbott said.
Lawmakers will replenish a federal disaster relief fund to keep aid flowing, but full assistance will come from Congress in installments, U.S. House of Representatives Speaker Paul Ryan said.
"The cash drain is fast. And so we're going to have to do some quick responses," Ryan said in an interview with radio station WCLO in his hometown Janesville, Wisconsin.
Moody's Analytics estimated the economic cost from Harvey for southeastern Texas at $51 billion to $75 billion.
(Additional reporting by Richard Valdmanis, Ernest Scheyder, Ruthy Munoz, Peter Henderson and Andy Sullivan in Houston, Steve Holland in Washington, David Gaffen in New York, Jon Herskovitz in Austin, Texas, and Brendan O'Brien in Milwaukee; Writing by Scott Malone and Dan Whitcomb; Editing by Bill Trott and Jonathan Oatis)