According to the Dallas Fire Department, the three fatalities included two women and one child. Fire officials say that the three injured victims included two taken by ambulance and one critical.
Firefighters and other first responders swarmed around the fire at the apartment complex after a gas leak leveled the building and set it ablaze.
According to the Dallas Police Department, the fire was reported in the 400 block of East 9th Street in the Oak Cliff neighborhood on Thursday afternoon.
Crews were first responding to the scene for a gas leak at 12:47 p.m., and two minutes later, they arrived. That's when officials say the explosion happened and the fire erupted.
The five-alarm response brought nearly 100 firefighters to the scene to help contain the flames and protect nearby residents, officials said.
Images shot from over the fire response showed smoke rising into the sky from large piles of debris.
Police said that a family assistance center was established at a high school near the scene, and urged families to go there instead of the active fire scene to obtain assistance and information.
A neighbor told ABC affiliate WFAA that the explosion blew out the windows of her nearby apartment and that she was shaken by the experience, adding that it sounded like a bomb had gone off.
Only 35-40% of the apartment debris has been checked, fire officials said.
Fire officials say that there could be more fatalities as the search continues.