(Adds details on fire at chemical plant)
LAKE CHARLES, La./HOUSTON, Aug 31 (Reuters) - The remnants of Tropical Storm Harvey drenched northern Louisiana on Thursday as it moved inland, leaving rescuers to search homes around Houston and in the hard-hit southeastern Texas coast for more survivors and victims.
The storm killed at least 35 people and its aftermath - including an explosion and dangerous smoke at a chemical plant and swollen rivers and reservoirs - threatened more misery for residents of Texas and Louisiana.
Harvey's death toll was rising as bodies were found in receding waters. Some 32,000 people were forced into shelters around the U.S. energy hub of Houston since it came ashore on Friday as the most powerful hurricane to hit Texas in a half-century.
Storm-related power outages prompted two explosions at a flood-hit Arkema SA chemical plant in Crosby, Texas, 30 miles (48 km) northeast of Houston, with one sheriff's deputy sent to the hospital after inhaling chemicals as smoke plumes rose 40 feet (12 m) in the air.
"The plume is incredibly dangerous," Federal Emergency Management Agency Administrator Brock Long told reporters.
A company official described the smoke as a noxious irritant created after refrigeration systems on a truck used to store the chemicals failed, causing them to overheat. Eight more trucks also storing the chemicals also could explode, public safety officials and a company executive told reporters.
"These things are going to catch on fire. They are going to burn with intensity," said Bob Royall, assistant chief of emergency operations at the Harris County Fire Marshal's Office. "Most of the material is going to be consumed by a very hot fire."
A 1.5-mile (2.4 km) radius around the plant had been evacuated and the company urged people to stay away from the area.
DOWNGRADED TO DEPRESSION
By Thursday, Harvey was downgraded to a tropical depression, located about 15 miles (24 km) south of Monroe, Louisiana. The storm's rains wrought the most damage along the Gulf Coast and the National Weather Service warned as much as 10 inches (25.4 cm) could fall in Mississippi, Tennessee and Kentucky.
Rivers and reservoirs in Texas remained at or near flood level, with officials warning high water would remain a danger for the next few days.
Federal officials already have rescued 10,000 people from flooded homes and would continue to search, Brock said.
The Houston Fire Department will begin a block-by-block effort on Thursday to rescue stranded survivors and recover bodies, Assistant Fire Chief Richard Mann told reporters.
Nine members of the ad-hoc "Cajun Navy" - volunteers towing boats behind pickup trucks - gathered in Lake Charles early on Thursday, deliberating whether they could safely get in to badly flooded parts of coastal southeastern Texas, including Orange, Port Arthur and Beaumont.
"You can't get anywhere by vehicle," said Troy Payne, 56, who had driven in from Atlanta. "To me, this is a helicopter function from here on out unless the water level falls."
Nearly 30 inches (76.2 cm) of rain hit the Port Arthur area.
Beaumont said it had lost its water supply due to flood damage to its main pumping station.
Fort Bend County ordered a mandatory evacuation on Thursday for areas near the Barker Reservoir, which was threatening to flood. The reservoir is about 20 miles (32 km) west of Houston.
Police in Houston's Harris County said 17 people remained missing.
Some 325,000 people and businesses already had applied for FEMA assistance and the agency already has paid out $57 million in aid, Brock said.
'NOT MY HOUSE ANYMORE'
Anita Williams, 52, was among dozens of people lined up Thursday morning at a shelter at Houston's George R. Brown Convention Center to register for FEMA aid. She said she had returned to her neighborhood on Wednesday to survey the damage to her one-story house.
"It's not my house anymore. My deep freezer was in my living room," she said, her voice breaking.
Williams said she had been trapped on the Houston Ship Channel bridge overnight on Saturday in her Toyota Camry before she was rescued Sunday by a man in a large truck. Her fiancé, a disabled man, had to be rescued from their house as waters rose to chest level and joined her.
Flooding shut the nation's largest oil refinery in Port Arthur in the latest hit to U.S. energy infrastructure that has sent gasoline prices climbing and disrupted global fuel supplies.
The storm prompted the U.S. Energy Department to authorize the first emergency release of crude oil from the Strategic Petroleum Reserve since 2012. Some 500,000 barrels of oil will be delivered to a Phillips 66 refinery in Louisiana unaffected by the storm, an Energy Department spokeswoman said.
Average U.S. retail gasoline prices have surged to $2.449 per gallon nationwide in the storm's wake, up 10.1 cents from a week ago, the AAA said on Thursday.
Moody's Analytics estimated the economic cost from Harvey for southeast Texas at $51 billion to $75 billion, ranking it among the costliest storms in U.S. history.
At least $23 billion worth of property has been affected by flooding from Harvey just in parts of Texas' Harris and Galveston counties, a Reuters analysis of satellite imagery and property data showed.
Governor Greg Abbott warned floodwaters would linger for up to a week. The area affected is larger than that hit by 2005's Hurricane Katrina, which killed more than 1,800 people in New Orleans, and 2012's Superstorm Sandy, which killed 132 around New York and New Jersey, he said.
U.S. Vice President Mike Pence and several Cabinet secretaries will travel to Texas on Thursday to meet residents affected by the storm.
(Additional reporting by Richard Valdmanis, Mica Rosenberg, Marianna Parraga, Gary McWilliams, Ernest Scheyder, Erwin Seba, Ruthy Munoz, Peter Henderson and Andy Sullivan in Houston, David Gaffen and Christine Prentice in New York, Susan Heavey in Washington, Jon Herskovitz in Austin, Texas, and Brendan O'Brien in Milwaukee; Writing by Scott Malone and Jon Herskovitz; Editing by Lisa Von Ahn and Bill Trott)