The plant was shut down on Friday before Hurricane Harvey arrived and the company left almost a dozen of people there to ensure the safety of chemicals.
Thick, black smoke poured out of two trailers with organic peroxides at the Arkema plant in Crosby, east of Houston, on Friday evening.
The first of the nine containers caught fire and burned for nine hours overnight Wednesday into Thursday.
Arkema says Harvey's floodwaters engulfed its backup generators and knocked out the refrigeration necessary to keep the compounds from degrading and catching fire.
Before the local authorities made a decision to evacuate residents of Crosby because of the threat of explosion at a chemical plant.
The safest option is to "let these fires happen and let them burn out", company spokeswoman Janet Smith said Friday.