HOUSTON (AP) - HOUSTON (AP) -- Firefighters began a block-by-block search of tens of thousands of flooded Houston homes Thursday to look for anyone who might have been left behind in Harvey's fetid floodwaters, and the loss of power at a chemical plant set off explosions that prompted a public health warning.
Searchers will also be looking for any bodies that could add to the confirmed death toll of at least 31. They said it could take up to two weeks to check all neighborhoods that were submerged by more than 4 feet of rain.
As the water began to recede in the nation's fourth-largest city, the threat of major damage from the storm shifted to a region near the Texas-Louisiana state line.
The fires and two explosions that rocked the Arkema Inc. plant northeast of Houston ignited a 30- to 40-foot flame and sent up a plume of smoke that the head of the Federal Emergency Management Agency initially described as "incredibly dangerous." FEMA later backed away from that statement, saying that Administrator Brock Long issued the warning out of an abundance of caution.
An Environmental Protection Agency analysis of the smoke showed it posed no immediate threat to public health, the agency said.
The French operator of the plant feared that up to eight more chemical containers could burn and explode.
In Houston, the latest surveys indicated that the storm and floodwaters have caused major damage to more than 37,000 homes and destroyed nearly 7,000, the Texas Department of Public Safety reported.
The confirmed death toll now includes six family members - four of them children - whose bodies were pulled Wednesday from a van that had been swept off a Houston bridge into a bayou.
Farther east, Beaumont and Port Arthur struggled with rising water after being pounded with what remained of the weakening storm. Beaumont lost water service after its main pump station was overwhelmed by the swollen Neches River. That forced Baptist Beaumont Hospital to airlift nearly 200 patients to other facilities.
Port Arthur found itself increasingly isolated as floodwaters swamped most major roads out of the city. More than 500 people - along with dozens of dogs, cats, a lizard and a monkey - took shelter at the Max Bowl bowling alley, general manager Jeff Tolliver said.
"The monkey was a little surprising, but we're trying to help," he said.
The chemical plant in Crosby lost power after the storm, leaving it without refrigeration for chemicals that become volatile as temperatures rise. Arkema shut down the plant before Harvey made landfall.
The blasts were small and that some deputies suffered irritated eyes from the smoke, fire officials said.
In the largely rural area surrounding the plant, authorities went door to door to explain the situation and called on residents to evacuate, but leaving was not mandatory.
Floodwaters also toppled two oil storage tanks in South Texas, spilling almost 30,000 gallons (114,000 liters) of crude. It was not immediately clear whether any of the spilled oil was recovered. More damage to the oil industry infrastructure is expected to emerge as floodwaters recede.
Forecasters downgraded Harvey to a tropical depression late Wednesday from a tropical storm, but it still has lots of rain and potential damage to spread, with 4 to 8 inches (10 to 20 centimeters) forecast from the Louisiana-Texas line into Tennessee and Kentucky through Friday. Some spots may get as much as a foot, raising the risk of more flooding.
For much of the Houston area, forecasters said the rain is pretty much over.
"We have good news," said Jeff Lindner, a meteorologist with the Harris County Flood Control District. "The water levels are going down."
Residents were warned about the dangers of heat exhaustion if they have lost power or must toil outdoors, with temperatures expected to climb into the low 90s through the weekend.
Houston's two major airports were up and running again Wednesday. Officials said they were resuming limited bus and light rail service as well as trash pickup.
At Hermann Park, south of downtown, children glided by in strollers and wagons, joggers took in midday runs and couples walked beside cascading fountains and beneath a sparkling sun. People pulled into drive-thru restaurants and emerged from a store with groceries.
At the same time, many thousands of Houston-area homes are under water and could stay that way for days or weeks. And Lindner cautioned that homes near at least one swollen bayou could still get flooded.
Houston-area 911 centers are getting more than 1,000 calls an hour from people seeking help, officials said.
Altogether, more than 1,000 homes in Texas were destroyed and close to 50,000 damaged, and over 32,000 people were in shelters across the state, emergency officials reported. About 10,000 more National Guard troops are being deployed to Texas, bringing the total to 24,000, Gov. Greg Abbott said.
In Orange, Texas, about 30 miles (50 kilometers) east of Beaumont, residents of a retirement home surrounded by thigh-deep water were rescued by National Guardsmen and wildlife officers, who carried them from the second floor and put them aboard an airboat.
Harvey initially came ashore as a Category 4 hurricane in Texas on Friday, then went back out to sea and lingered off the coast as a tropical storm for days, inundating flood-prone Houston.
Harvey's five straight days of rain totaled close to 52 inches, the heaviest tropical downpour ever recorded in the continental U.S.
Associated Press writers Frank Bajak, Matt Sedensky and Michael Graczyk in Houston; Diana Heidgerd and David Warren in Dallas; Seth Borenstein in Washington; Paul J. Weber in Austin, Texas; and Tammy Webber in Chicago contributed to this report.