DALLAS (AP) — Authorities say eight people were injured, including four firefighters, in a Dallas apartment complex explosion.

Dallas Fire-Rescue says three firefighters were injured critically, while the other has been discharged after receiving hospital treatment for minor injuries.

Four civilians also were hospitalized in stable condition.

Fire officials say the firefighters were investigating a report of a natural gas leak at the two-story complex in southern Dallas.

They had reported smelling gas just before the explosion partially collapsed the building.

The cause of the blast hasn't been determined and remains under investigation.