A huge fire has destroyed a two-storey apartment building in Dallas, Texas causing fatalities and injuring at least four people, as the search for the missing continues.

The blaze sent huge plumes of black smoke into the sky and drew a massive firefighter response.

"There have been fatalities at this point," Dallas Fire-Rescue Deputy Chief Mark Berry said at a news conference on Thursday, 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 smouldering rubble of the building on the outskirts of downtown Dallas on Thursday afternoon, 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.

City officials said there was no city maintenance work being done at the scene at the time of the explosion.

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.

Authorities set up a family reunification centre at a nearby high school.