Four Dallas firefighters and four residents were injured in an explosion Wednesday at an apartment complex that caused the partial collapse of a building, officials said. 

The complex exploded into flames after firefighters arrived just after 10:20 a.m. for a reported gas leak at the Highland Hills Apartments on Highland Hills Road in South Dallas. Dallas Mayor Eric Johnson reported that four firefighters and three civilians were injured.

Authorities later reported that a fourth resident was injured. 

Several Dallas firefighters and some residents were hurt Wednesday during an explosion. 

Several Dallas firefighters and some residents were hurt Wednesday during an explosion.  (KDFW)

Two firefighters were listed in critical condition. Two other firefighters and three residents were listed in stable condition, Evans said, adding that one firefighter was eventually released from a hospital.  

Fire crews initially responded to reports of a natural gas leak. While investigating the source of a gas odor, an explosion occurred, Dallas Fire Rescue Department spokesman Jason Evans told reporters. Witnesses told fire personnel they smelled gas in the area as early as Tuesday night, he said. 

All residents of the building were accounted for, according to the department. 

The western portion of the two-story apartment building was heavily damaged, Evans said. 

"The damage looks pretty significant," Evans said. "Officially, we cannot imagine that there would be anything to salvage as it relates to the building going forward."

The cause of the explosion has not been determined.

Dallas fire crews respond to an explosion Wednesday. 

Dallas fire crews respond to an explosion Wednesday.  (KDFW)

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Workers with Dallas-based Atmos Energy and hazmat crews responded to the fire as well as multiple local, state and federal agencies.