A tank holding a flammable chemical caught on fire at a Texas plant, killing one worker, critically injuring two others and sending other panicked employees fleeing over a fence to safety.

Harris County Sheriff Ed Gonzalez confirmed the fatality in a tweet and said the two injured had been taken by helicopter to a hospital.

They were in critical condition, said Rachel Moreno, spokeswoman for the Harris County Fire Marshal's Office.

Authorities shut down a road near the fire at a KMCO chemical plant in Crosby, about 40km northeast of Houston, Gonzalez said.

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All residents within a 1.6km radius of the plant were ordered to stay indoors or shelter in place.

Harris said a transfer line ignited in the area of a tank of isobutylene — a flammable colourless gas used in the production of high octane gasoline — which then caught on fire. First Responders were trying to contain the fire, Gonzalez said.

Worker Justin Trahan told Houston television station KPRC that he heard "some panic on the radio" but no alarms sounding before the plant caught fire.

"We didn't think anything of it — we didn't think it was anything severe," he said.

Trahan said employees began running after "the tank ignited".

He said that he and other colleagues had to jump over a fence to escape because all the gates were locked.

John Foley, chief executive of KMCO, said in a statement that the company had activated its emergency response team and set up a command centre.

"We are working with local first responders to extinguish the fire," he said.

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KMCO is a chemical company that offers coolant and brake fluid products and chemicals for the oilfield industry.

The Crosby, Sheldon and Channelview school districts asked students and staff to shelter in place at all their campuses.

The Texas Commission on Environmental Quality said that it has dispatched emergency response personnel to conduct an initial assessment of the fire.

The fire comes about two weeks after a March 17 blaze at a petrochemical storage facility in Deer Park , located about 32km south of Crosby. That earlier fire burned for days and triggered air quality warnings.

- AP