At least two people were killed and several others were injured in a chemical leak at a Texas LyondellBasell facility, authorities said.

LyondellBasell, a plastics and chemical company, said in a statement that its La Porte complex suffered an acetic acid leak at about 7:35 p.m. Tuesday in a unit shut down earlier in the day for planned maintenance, causing two contractors to sustain fatal injuries. Another five contractors and an employee were sent to local hospitals to receive medical treatment for burns, the company said.

The Harris County Fire Marshal's Office said the leak has since been isolated and that air monitoring at the facility perimeter shows no offsite contamination.

Harris County Fire Marshal Laurie Christensen told reporters during an evening press conference that the chemicals involved in the leak, which are used in food-grade vinegar, can cause severe burns and are toxic if inhaled.

Thirty-one people were being evaluated for injuries and symptoms, five were being treated on scene and one person was transferred to the hospital by LifeFlight and another by ambulance, she said.

"We don't really know much about it. We don't know how it occurred but we do know we have injuries and we do know we have fatalities," she said.

Christensen had said the leak was caused by a small explosion in the plant, but her office later clarified that investigators had ruled out an explosion as the cause of the leak following a preliminary inspection of the site.

All personnel working within the unit where the leak occurred have been accounted for, LyondellBasell said.

"The leak is stopped and clean-up is in progress," the company said.

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