Officials are investigating what caused a fire that killed two people and displaced multiple residents at an apartment building in Washington, D.C., early Tuesday.

The two that died, a man and a woman, had been taken to the hospital in critical condition, but succumbed to their injuries, according to D.C. Fire and EMS.

The two-alarm fire began early Tuesday on the third floor of the apartment building in Southwest Washington, D.C., the fire department said.

After arriving at the scene, around 100 firefighters were able to knock down the fire and get all of the residents out of the building, according to the fire department.

Fire officials said Tuesday that there are 40 apartments deemed uninhabitable due to the fire. Residents are being assisted with housing options.

They said they will return to the scene to distribute fire prevention information and test all smoke alarms, replacing or installing new ones as needed.