At least one person has been killed and dozens more are hurt, some of them critically, after a massive explosion at a chemical plant in Louisiana. NBC's Mark Potter reports.

An explosion and fire at a Louisiana chemical plant Thursday morning killed one person and injured 73 more, Gov. Bobby Jindal said.

The explosion took place at Williams Olefins chemical plant in Ascension Parish, between Baton Rouge and New Orleans, state police said. A fire after the explosion was contained and then extinguished, and preliminary tests showed the air was safe.

Chemicals were being burned off, but there was no immediate threat to the public, said Jared Sadifer, a state police spokesman.

The fire, fueled by the petrochemical propylene, burned for more than three hours, though government monitors had yet to detect dangerous levels of emissions, Jindal told a news conference near the scene.

WVLA People run away from an explosion and fire at the Williams Chemical Plant in the Ascension Parish town of Geismar, La., on June 13. The photo was taken by a plant employee who did not wish to be identified.

"Once the investigations are done, once there's a responsible party, they will absolutely be held responsible," Jindal said.

The cause of the fire was undetermined, Slaton said. Hazardous-materials crews were checking the site, and a controlled fire was burning off the rest of the chemicals.

The injured were taken to hospitals, and a total of 300 workers were evacuated, Jindal said. Ten people remained in a safe room at the plant, he said.

The man killed was identified Thursday evening as 29-year-old Zachary C. Green of Hammond, Louisiana, according to the state police.

Authorities ordered people within a 2-mile radius to remain in their homes, in part because of the smoke, said Lester Kenyon, a spokesman for Ascension Parish.

The site of the explosion remained an “active scene,” Lester Kenyon, a public information officer for Ascension Parish, told NBC News. He said the parish’s emergency operations center was in “partial activation,” with police, fire, Homeland Security and other emergency officials on the scene.

Baton Rouge General Medical Center said it had received seven victims, and St. Elizabeth Hospital in Gonzales had eight more. Eleven were taken to Our Lady of the Lake Regional Medical Center in Baton Rouge, two in critical condition. Some patients were flown from the scene.

Joseph Chamberlain / Red Stick Storm Spotters A plume of smoke rises from an explosion at the Williams Olefins chemical plant on Thursday.

The plant said the blast happened just after 8:30 a.m. Emergency responders were notified and shut-down valves were closed after the explosion, isolating the unit, according to a release.

The plant is in the unincorporated, mostly industrial area of Geismar, about 60 miles northwest of New Orleans. The facility produces 1.3 billion pounds of ethylene and 90 million pounds of propylene a year, according to the company’s website.

Reuters contributed to this report

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