Exxon Mobil emergency response teams have extinguished a fire at the Baytown Refinery in Baytown, Texas.
"Our first priority is people in the community and in our facilities," Exxon Mobil Baytown Area said in a statement on Twitter.
The company said there has been no adverse air quality monitoring impacts to the community.
"Around 1 a.m. on 12/23/2021, a fire occurred at our facility," the company said on social media. "At this time, emergency vehicles and smoke may be noticeable to the community. We are coordinating with local officials, and working to resolve the issue as soon as possible."
The causes of the incident have not yet been determined, according to Exxon Mobil. The company is working with authorities.
"All findings will be incorporated in our continuing effort to enhance our safety performance," the company stated.
An information line has been set up for anyone affected by this incident at 1-800-241-9010.
Authorities in Texas said they were investigating a "major industrial accident" at the Exxon Mobil plant on Thursday morning.
"Some injuries have been reported. Please avoid the area," the Harris County Sheriff's Office said on Twitter.
Initial reports indicated some type of explosion occurred inside the plant, Sheriff Ed Gonzalez said. Four people were injured, with three taken from the scene by Lifeflight and one by ambulance, he said.
Videos posted on social media showed dense smoke rising from the facility.
"My mom lives right behind the plant and around 1 a.m. I heard a loud 'boom' and the house shaking," Kendall Merritt, who lives nearby, told ABC News. "The sound was as if someone had slammed a door right in my ear."
Exxon Mobil's Baytown complex covers 3,400 acres about 25 miles east of Houston, according to the company's website. Its local refinery can process about 584,000 barrels of crude oil each day.
Gonzalez said there wasn't an order for nearby residents to evacuate or shelter-in-place.