Explosions at a chemical plant near Houston pose fresh worries for storm-battered Texas as rescuers search block by block for survivors of Hurricane Harvey.
The death toll from Hurricane Harvey has risen to 35 people.
The explosions in Crosby, Texas, are the latest aftermath of the historic flooding brought by the most powerful storm to land in Texas in a half-century, which drove tens of thousands from their homes around the US energy hub.
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Portions of the state's southeastern coast remain largely cut off because of flooded roadways, even as some commuters began to return to the streets of parts of Houston.
In Crosby, about 48km northeast of Houston, a sheriff's deputy was taken to a hospital after being exposed to the 12m-high smoke plume that erupted when chemicals stored at a Arkema SA plant erupted into flames after the refrigerator cooling the truck trailer they were stored in failed.
After the multiple blasts, local public safety and company officials insisted there was no risk to the public outside the 2.4km safety perimeter, even though they said eight more trucks storing the same chemicals would eventually catch fire.
That was no comfort to Frances Breaux as she pleaded with police at the perimeter to check on an elderly married couple that live two streets from the plant. The couple, Leo and LeJane Opelia, both in their late 70s, were evacuated from their home but returned on Wednesday night to check on their cats and belongings, Breaux said.
Police said the potential for more blasts made it too dangerous to check on the couple.
"The plume is incredibly dangerous," Federal Emergency Management Agency Administrator Brock Long told reporters.
An Arkema 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.
By Thursday, Harvey was downgraded to a tropical depression, located about 15 miles (24km) south of Monroe, Louisiana, but there was potential for more flooding in the brimming rivers and reservoirs it left behind in Texas.
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.
Moody's Analytics estimated the economic cost from Harvey for southeast Texas at US$51 billion to US$75 billion, ranking it among the costliest storms in US history.
At least US$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.
The storm has drawn comparisons to 2005's Hurricane Katrina, which killed more than 1800 people in New Orleans, and 2012's Superstorm Sandy, which killed 132 around New York and New Jersey.