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.

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"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. "Let us work through the recovery phase and get a total number."

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.

Julie Jensen said she was at home less than a block from the burning building when she heard a noise like an explosion that left her ears ringing.

"I was sitting on my couch watching TV — stuff flew off our walls," Jensen said.

Jensen said she saw rising smoke and neighbors running when she looked out the window. She grabbed her family's cat and left, finding a nearby parking lot to wait until she knew it was safe to return.

Sal De La Rosa was at work at a nearby auto repair shop when "all of a sudden we just heard and felt this huge boom."

"We felt where the building kind of shook a little bit," Del La Rosa said.

He said a co-worker went outside and saw thick, black smoke rising into the air.