Emergency personnel administered first aid to employees and contractors at the scene. Although many had received minor burns, none were seriously injured and were released shortly afterward.
The fire, which was put out by the company employees, sent black smoke into the air over the complex in Baytown, a city of 75,000, located about 48 km east of Houston. Firefighters and equipment from the city entered the plant at midday to assist, an official said.
Firefighters continued to spray water on the site of the fire late Wednesday. Residents around the plant were told to close windows and doors, turn off air conditioning and remain in their homes or offices. Schools in several communities in the area kept summer students indoors.
ExxonMobil spokeswoman Natasha Barrett said, "We realize the people who live here in Baytown and our surrounding communities are worried. We understand that and we've been working hour after hour to check on things, to monitor air quality."
Aerial footage during the blaze showed flames and heavy smoke emanating from a large column at the facility, which Exxon identified as part of its production of olefins, a component of plastic. Emergency vehicles and people were massing around the edge of the complex.
By 6:35 p.m., the fire was contained, company officials said on Twitter.
The Baytown complex that includes the olefins plant where the fire occurred, employs about 7,000 people among four manufacturing sites that cover 1,375 hectares. The complex sits along the Houston Ship Channel, the nation’s largest and busiest energy port.