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At least one person was killed and 73 others were injured in a huge explosion followed by a fire at a chemical plant in Geismar, Louisiana, state Gov. Bobby Jindal said Thursday.

The accident's cause is not yet known, but more than 300 workers had to be evacuated from the industrial area and authorities asked local residents to remain indoors until the situation was brought under control.

Jindal said at a press conference that the plant had obtained approval for an expansion project and one of the work areas was in the process of renovation, adding that an investigation would be launched into the "tragic incident."

Louisiana Department of Environmental Quality (DEQ) Assistant Secretary Cheryl Nolan said that the plant had had some past problems regarding compliance with safety regulations, and she added that her team will study the incident to determine if there was any negligence on the part of The Williams Companies Inc. - the plant's owner - based in Tulsa, Oklahoma.

At the time of the blast, there were about 600 workers at the plant, State Police Capt. Doug Cain said.

The injured were taken by ambulance and helicopter to hospitals in the area.

The explosion occurred shortly after 8:30 a.m. and two hours later police blocked off the surrounding roadways.

At 1 p.m., state police said that the fire had been extinguished and that the situation was under control.

The state DEQ sent teams to the site to evaluate the air quality, given that toxic chemicals are produced at the plant and could have been released, spokeswoman Jean Kelly said.

The firm's Geismar plant produces some 600 million kg (1.3 billion pounds) of ethylene and 40 million kg (90 million pounds) of polymer grade propylene every year, both of which are colorless and flammable gases that are widely used in the chemical industry.

According to State Police Chief Mike Edmonson, the substance that caught fire was the propylene.

The explosion at the Louisiana facility is the second at a U.S. chemical plant in the past two months. In mid-April, a fertilizer plant in West, Texas, exploded, destroying 50 homes and killing 15 people, most of them volunteer firefighters who were trying to put out the resulting blaze. The cause of the blast is still under investigation. EFE