sending up a plume of acrid, eye-irritating smoke and adding a new hazard to Hurricane Harvey's aftermath.
The plant's owners warned more explosions could follow because a lack of refrigeration was causing chemicals stored there to degrade and burn.
The top federal emergency official in Washington warned that the plume of smoke was "incredibly dangerous." But local officials disputed that.
There were no immediate reports of any serious injuries.
Dozens of workers were pulled out of the Arkema Inc. plant before the hurricane hit and a small crew that had been left behind was evacuated before the blasts for fear of just such a disaster. Officials had also ordered people living within 1½ miles (2.4 kilometers) to leave on Tuesday.
Fire and plant officials said the substances that caught fire were organic peroxides, a family of volatile compounds used for making a variety of products, including pharmaceuticals and construction materials.
Earlier this week, Arkema warned of the possibility of an explosion at the plant about 25 miles (40 kilometers) northeast of Houston, saying Harvey's floodwaters had knocked out power and backup generators, disabling the refrigeration needed to keep the organic peroxides stable.
On Thursday, Rich Rennard, an Arkema executive, said the chemical compounds were transferred to refrigerated containers after power was lost. But he said those containers also failed, causing the chemicals to degrade and burn in one unit before dawn.
He said the company expected more explosions from the eight remaining containers.
Assistant Harris County Fire Chief Bob Royall said the organic peroxides caught fire in a tractor-trailer and sent up 30- to 40-foot (9- to 12-meter) flames and black smoke. Harris County Fire Marshal spokeswoman Rachel Moreno put the quantity of burning organic peroxide at 2 tons.
Sheriff Ed Gonzalez said some deputies suffered eye irritation from the smoke, but added: "It is not anything that we feel is a danger to the community at all."
In Washington, however, Brock Long, administrator of the Federal Emergency Management Agency, told reporters that "by all means, the plume is incredibly dangerous."
Arkema had warned earlier this week that the chemicals would erupt in an intense fire resembling a gasoline blaze. There was "no way to prevent" the explosion, CEO Rich Rowe said on Wednesday.
The company shut down the site before Harvey blew ashore, though a crew of 11 had stayed behind until it, too, was pulled out.
The plant is along a stretch near Houston that contains one of the biggest concentrations of refineries, pipelines and chemical plants in the country.
Moreno, of the fire marshal's office, said the 1½-mile radius was developed in consultation with the Homeland Security Department and other experts.
"The facility is surrounded by water right now so we don't anticipate the fire going anywhere," she said.
Arkema was required to submit a risk management plan to the Environmental Protection Agency because it has large amounts of sulfur dioxide, a toxic chemical, and methylpropene, a flammable gas. The plans are supposed to detail the effects of a potential release and how the company would respond.
In its most recently available submission from 2014, Arkema said that in a worst-case scenario, 1.1 million residents could be affected over 23 miles (37 kilometers), according to information compiled by a nonprofit group and posted on a website hosted by the Houston Chronicle.
Arkema said that scenario was highly unlikely because it assumed that all of the plant's safety measures failed and that strong winds were blowing directly toward Houston, the nation's fourth-largest city.