A chemical plant near the flooded city of Houston is expected to explode or catch fire in the coming days.
During heavy rainfall from Hurricane Harvey, the Arkema plant at Crosby lost refrigeration of chemical compounds which need to be kept cool, and there is no way to prevent a possible fire, the company said.
At least 33 people have been killed in the aftermath of the storm.
US energy supplies have also been hit, as oil companies shut down pipelines.
The US National Weather Service downgraded the former hurricane to a tropical depression but has forecast continuing heavy rainfall over eastern Texas and western Louisiana.
What happened at the chemical plant?
The Arkema chemical plant shut down its production on Friday, before the storm made landfall.
But 40in (102cm) of rainfall in the area flooded the site and cut off its power, the company said in a statement. Backup generators were also flooded.
The facility manufactures organic peroxides, and chemicals stored on site can become dangerous at higher temperatures.
“Any fire will probably resemble a large gasoline fire,” CEO Richard Rowe told Reuters news agency. “The fire will be explosive and intense.”
He said the black smoke produced would irritate skin, eyes and lungs.
“The high water that exists on site, and the lack of power, leave us with no way to prevent it.”
The fire is expected to be mostly contained to the site itself but residents of Harris County have been evacuated in a 1.5 mile (2.4 km) radius around the plant as a precaution.
The last remaining workers at the site were evacuated on Tuesday.
How are rescue efforts progressing?
Parts of Texas have been hit by more than 50in of rainfall since Hurricane Harvey landed, setting new records before it was downgraded to a tropical storm and, late on Wednesday, to a tropical depression.
Rescue efforts continued overnight. Thousands of people have been rescued from floodwater throughout the state, and more than 32,000 people are still in emergency shelters.
Houston, the fourth most populous city in the US, was badly hit, and large parts remain underwater.
The city is also a key energy hub. The storm and its subsequent flooding has knocked out about a quarter of the country’s refining capacity, sending petrol prices to a two-year high.
INTERACTIVESee how flood waters caused by Hurricane Harvey have covered low-lying areas
Port Arthur, about 80 miles east of Houston, was also severely flooded. Mayor Derrick Freeman, posting on Facebook, said the entire city was underwater, and appealed for anyone who owned a boat to help.
Details of some of the deaths in Texas have emerged:
- In Beaumont, north-west of Port Arthur, rescue teams saved an 18-month old girl found clinging to her dead mother in the floodwaters
- In Harris County, a family of six – two great-grandparents and four children – drowned while trying to flee the floods in a van
- A married couple drowned when their truck was swept away while they were on the phone to emergency services asking for help, the Associated Press reports
On Tuesday, Houston implemented a curfew in a bid to prevent looting of abandoned homes. Port Arthur followed suit Wednesday.
What happens next?
An additional 10,000 members of the National Guard were said to be on their way to Texas to join the rescue efforts, adding to the 14,000 already deployed.
Harvey was the most powerful hurricane to hit Texas in more than 50 years when it first made landfall at Corpus Christi, 220 miles south-west of Houston, late on Friday.
At a press conference Wednesday, Texas Governor Greg Abbott said the state could need more than $125bn (£97bn) from the federal government to help its recovery.
And he warned “the worst is not yet over”, as flooding was expected to continue for several days.
Meanwhile, the tropical depression is now moving north-north-east, the US National Weather Service said.
Heavy rainfall is expected from Louisiana to Kentucky over the next three days, and flood warnings remain in effect for south-east Texas and parts of south-west Louisiana.