By Arpan Varghese

(Reuters) -Four people were injured when a fire erupted on Thursday morning at an Exxon Mobil Corp complex in Baytown, Texas, one of the largest refining and petrochemical facilities in the United States.

There were no fatalities and those injured were in a stable condition, while other personnel were accounted for, Exxon said.

Emergency response teams were working to extinguish the blaze more than five hours after it erupted at about 1 a.m. on Thursday, the company said.

The fire occurred in a hydrotreater unit at the oil refinery that had been shut on Wednesday due to a bypass line leak, people familiar with plant operations told Reuters. The injured were contractors who had been repairing the leak.

Three of the injured were flown to hospital by Lifeflight rescue helicopter and a fourth person was taken by ambulance, Harris County Sheriff Ed Gonzalez said on Twitter.

He said initial reports had indicated there had been some type of explosion at the plant. Social media users said on Twitter that a blast shook buildings in the area.

An Exxon official told a news conference the blaze had affected a unit that produces gasoline.

The Baytown plant houses a chemical plant, an olefins plant and the country’s fourth biggest oil refinery, with capacity to process 560,500 barrels per day of crude.

The facility spans about 3,400 acres along the Houston Ship Channel, about 25 miles (40 km) east of Houston and employs about 7,000 people.

The olefins facility, which began operations in 1979, is one of the largest ethylene plants in the world, according to the company’s website.

Production was reduced across the Baytown refining and petrochemical complex in August 2019 because of a fire in a propylene recovery unit at the olefins plant.

As many as 37 workers were injured in another fire at the olefins facility in July 2019.

(Reporting by Arpan Varghese, Bharat Govind Gautam, Akriti Sharma and Shubham Kalia in Bengaluru, Erwin Seba in Houston; Additional reporting by Paarth Gururajan and Seher Dareen; graphic by Vijdan Mohammad Kawoosa; Editing by Edmund Blair and Kirsten Donovan)