DALLAS (AP) — An explosion at a Dallas apartment building engulfed the two-story complex in a towering and deadly blaze Thursday, shaking nearby homes and flinging debris. A search for the missing remained ongoing hours after the flames were brought under control, officials said.

Authorities would not provide an immediate number of deaths but confirmed there were fatalities. It was unclear how many residents lived in the building in the Oak Cliff neighborhood of Dallas, where some people said they had been unable to find or reach friends and family members.

“There have been fatalities at this point,” Dallas Fire-Rescue Deputy Chief Mark Berry said at a news conference, adding the mission has changed from rescue to recovery.

Dozens of firefighters searched through the smoldering rubble of the building on the outskirts of downtown Dallas, even as colleagues continued to drench the blackened debris.

Berry said firefighters were responding to a call of a gas leak when an explosion happened.

“We had the cavalry coming,” Berry said. “But the explosion had already taken place.”

Atmos Energy, a natural gas provider, said in a statement they were told by fire officials that a construction crew unrelated to the company had damaged a pipeline near the site of the fire.

Natural gas service to the area remained shut off, and company officials were working with investigators on-site, the company said.

Authorities set up a family reunification center at a nearby high school. Several hours after the blaze, Frances Rizo was still trying to find her friend who lived in the building.

“She’s not answering her phone,” Rizo said.

Firefighters rushed to the scene as flames and black smoke billowed into the sky. Some trained their hoses on piles of smoking debris while others removed lumber and other burned wreckage to look for anyone trapped underneath. Little more than a blackened shell of the original building remained.

“The fire is contained, but our members are still working on the scene to do primary searches,” said Dallas Fire-Rescue Assistant Chief James Russ.