Two explosions have occurred at the flood-hit Arkema SA chemical plant in Crosby, Texas, and there is a risk of further blasts.
The Arkema plant makes organic peroxides used in the production of plastic resins, polystyrene, paints and other products.
“Please do not return to the area within the evacuation zone until local emergency response authorities announce it is safe to do so,” it added.
The sheriff said one of its deputies was taken to hospital after inhaling fumes and nine other people drove themselves to hospital as a precaution.
The flooded facility had lost power and backup generators, leaving it without refrigeration for chemicals that become volatile as the temperature rises.
The company evacuated remaining workers at the damaged plant on Tuesday, and Harris County ordered the evacuation of residents within a 1.5-mile radius due to the risk of an explosion and subsequent leak.