DALLAS - Seven people, including four firefighters, were injured Wednesday when an apartment building exploded due to a natural gas leak.

WFAA reported that the firefighters were checking on the gas leak in the building around 10:20 a.m. when the building exploded.

Dallas Fire-Rescue firefighters said they smelled gas near the building's gate, and the building burst into flames when they started looking for the source.

WFAA said the fire was out around noon and three of the firefighters injured are in critical condition.

An official cause of the explosion has not been released, but a resident of the apartment building told firefighters they smelled gas in the building Tuesday night.