One person died and at least two others were critically hurt in an explosion and fire at a Texas chemical plant when a tank holding a flammable chemical caught fire. Harris County Sheriff Ed Gonzalez confirmed the fatality in a tweet and said the two injured had been taken by helicopter to a hospital.

Authorities shut down a roadway Tuesday near the fire at the KMCO chemical plant, which is in Crosby, about 25 miles northeast of Houston, Gonzalez said. KMCO is a chemical company that offers coolant and brake fluid products and chemicals for the oilfield industry.

The explosion happened around 10:45 a.m. when a transfer line ignited a tank full of a chemical called isobutylene. The fire was fully contained after 4 p.m., according to CBS affiliate KHOU-TV.

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All residents within a one-mile radius of the plant were ordered to stay indoors or shelter in place. Four nearby school districts serving some 30,000 students was locked down.

Smoke from explosion is seen at the KMCO chemical plant on Tue., April 2, 2019. KHOU-TV

"It was terrifying. It was definitely terrifying ... I don't know ... there's always a danger but you never expect it to happen," an employee told KHOU-TV.

He said employees made a mad dash for the exits.

Worker Justin Trahan told Houston television station KPRC-TV 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 he and other colleagues had to jump over a fence to escape because all the gates were locked.

The fire comes about two weeks after a March 17 blaze at a petrochemical storage facility in Deer Park, located about 20 miles south of Crosby. That earlier fire burned for days and triggered air quality warnings.

"It is disturbing and it is problematic that we're seeing this incident in a facility, especially on the heels of" the fire in Deer Park, said Harris County Judge Lina Hidalgo, the county's top administrator.

Samantha Galle lives less than a mile away from the plant and said she heard and felt an explosion Tuesday.

"It shook everybody's house around here," the 23-year-old said.

Moreno said the Environmental Protection Agency has been testing air samples from the area around the plant and has not found any harmful readings.

In 2016, KMCO's corporate agents pleaded guilty to a federal criminal charge of violating the Clean Air Act. A plea agreement document stated that a plant employee made false entries in logs of air testing of tanks that were known to be leaking chemicals. Another employee then used those falsified logs to submit reports to the federal and state environmental authorities.

The document says the violation went on between 2008 and 2012. A year earlier, the EPA cited KMCO for failing to comply with regulations on its risk-management plan for the plant, but settled with the plant for a $2,700 penalty. Texas has served the plant with three notices of violation of a federal clean-air law since last August, the EPA website shows.