DEER PARK, Texas (AP) — A flame that towered over a southeast Houston suburb had subsided Tuesday, but continued to burn following a massive pipeline explosion after a vehicle drove through a fence and struck an above-ground valve, officials said.

“Progress has been made as first responder crews worked through the night. The fire is significantly smaller,” according to a statement from the city of Deer Park.

City officials have said investigations by police and local FBI agents have found no preliminary reports that would suggest a coordinated or “terrorist” attack and that “this appears to be an isolated incident.”

The investigation included efforts to learn more about the driver of a vehicle that was incinerated by the pipeline explosion as flames scorched the ground across a wide radius, severed adjacent power transmission lines and ignited homes at a distance.

Police did not provide any information about the person’s condition.

An evacuation area included nearly 1,000 homes and initial shelter orders included schools.

The City of La Porte said it has slightly reduced the evacuation area south of the pipeline fire, but did not say how many people were affected.

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Operators shut off the flow of natural gas liquids in the pipeline, but so much remained in the miles of tubing that firefighters could do nothing but watch and hose down adjacent homes.

The statement by Deer Park said Energy Transfer, the Dallas-based owner of the pipeline, expects the fire to burn itself out later Tuesday.

Deer Park Mayor Jerry Mouton Jr. described intense heat from the fire that has continued burning for nearly 24 hours as ladder trucks showered houses from above.

Firefighters initially were dispatched Monday morning, after an explosion at a valve station in Deer Park, adjacent to La Porte, rattled homes and businesses, including a Walmart. Deer Park officials said an SUV drove into the valve after going through a fence on the side of the Walmart parking lot.

Deer Park spokesperson Kaitlyn Bluejacket has said four people were injured. She didn’t provide details about the severity of the injuries.

Harris County Judge Lina Hidalgo said in a statement that 20 miles (32 kilometers) of pipeline between the two closed valves had to burn off before the fire would stop.

Anna Lewis, who was walking into the nearby Walmart when the explosion happened, said it sounded “like a bomb went off.” She said everyone inside was rushed to the back of the store and then taken across the street to a grocery store before being bussed to a community center.

“It scared me,” she said. “You really don’t know what to do when it’s happening.”

Geselle Melina Guerra said she and her boyfriend heard the explosion as they were having breakfast in their mobile home.

“All of a sudden we hear this loud bang and then I see something bright, like orange, coming from our back door that’s outside,” said Guerra, who lives within the evacuation area.

Houston, Texas’ largest city, is the nation’s petrochemical heartland and is home to a cluster of refineries and plants and thousands of miles of pipelines. Explosions and fires are a familiar sight in the area, including some that have been deadly, raising recurring questions about the adequacy of industry efforts to protect the public and the environment.

Both Energy Transfer and Harris County Pollution Control are conducting air monitoring in the area and have found no health issues, according to Bluejacket, the Deer Park spokesperson, from the towering plume of fire and smoke that could be seen from at least 10 miles (16 kilometers) away at one point.

The Railroad Commission of Texas, which regulates oil and gas in the state, said its safety inspectors were investigating.

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AP writers Christopher L. Keller in Albuquerque, New Mexico, Valerie Gonzalez in McAllen, Texas, Sean Murphy and Ken Miller in Oklahoma City and Jamie Stengle in Dallas contributed to this report.