The explosion occurred at a Williams Partners' facility in Gibson, about 70 miles southwest of New Orleans.

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Explosion happens just before 11 a.m. at a natural gas plant in Gibson, Louisiana

4 people injured, including 2 in critical condition, a state police spokesman says

CNN  — 

An explosion rippled through a natural gas facility Thursday in south Louisiana, killing three people and sparking a fire that was still burning more than six hours later, authorities said.

The blast occurred just before 11 a.m. (noon ET) at a Williams Partners’ facility in Gibson, about 70 miles southwest of New Orleans. The plant was not fully functioning at the time, but people were there doing maintenance, the Louisiana State Police said on Facebook.

Fire crews and police retrieved three bodies and two “seriously injured” people, according to the state police.

Trooper Evan Harrell, a state police spokesman, later said four people were injured, two of whom are in critical condition. The 13 others at the facility were unharmed.

Williams Partners, in a statement provided by spokesman Chris Stockton, said “gas was not flowing through the pipeline system when the explosion occurred.”

The company added that none of its own workers suffered injuries and that “service to our customers has not been interrupted.”

It was not immediately clear what caused the explosion. Williams Partners said an “initial assessment … determined it does not appear to be a natural gas pipeline rupture (and) the building containing the compressor engines was not damaged.”

The fire at the site was still burning as of 6 p.m., though Harrell said it was contained and no one nearby had been told to evacuate.