DALLAS (AP) — A huge fire destroyed a two-story apartment building in Dallas on Thursday, injuring at least four people, sending plumes of black smoke into the sky and drawing a massive firefighter response, a fire official said.

Dozens of firefighters searched through the smoldering rubble of the building on the outskirts of downtown Dallas Thursday afternoon, even as colleagues continued to drench the blackened debris.The cause of the fire was not immediately known, but Assistant Chief James Russ of Dallas Fire-Rescue told a news conference that the blaze broke out after someone reported a gas leak. Neighbors said they heard a loud boom like an explosion. Russ said at least four people were taken to a hospital with injuries and that “it is unknown how many possible fatalities we may have.”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,” Russ said.