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.
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.
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.