A large fire at a petrochemical storage facility near Houston sent a thick black plume of smoke over the U.S.’s fourth-largest city on Monday and was expected to continue for days before burning out.

The fire at the Intercontinental Terminals Co. plant in Deer Park, Texas, first reported around 10:30 a.m. local time Sunday, had spread by Monday morning to seven storage tanks containing chemicals used as components of gasoline and lubricants, authorities said. No injuries had been reported.

Deer Park officials decided Monday morning to lift an earlier order for residents in the city of about 33,000, located about 18 miles east of downtown Houston, to shelter in place, noting that air quality monitoring near the fire site showed pollution below action levels.

First responders were actively working to contain the blaze, and taking steps to reduce what ITC described as a “minimal” risk of explosion. The company and local authorities were monitoring air quality from the fire, which by Monday had created a cone-shaped smoke cloud that was blowing over Houston and moving westward through the sky.

David Wascome, ITC’s senior vice president of operations, said the cause of the fire is still under investigation. The company said in a statement that particulate matter had been detected 6 miles southwest of the facility but that the readings were “well below hazardous levels.”