First responders had been working to put out the fire since 1 a.m. It was safely extinguished by about 9 a.m. Officials are continuing to monitor the air quality.

BAYTOWN, TX -- Fire at a Baytown ExxonMobil facility Thursday sent a massive plume of smoke into the air. At this point, it's not clear what started the fire.

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.