A dog was killed and 12 people were displaced in a north Phoenix apartment fire Saturday afternoon, fire officials said. 

The fire began inside an apartment at the Mountain View Casitas Apartments on Grovers Avenue and 12th Street and did significant damage to four units in the building, Phoenix fire officials said.

Two second-story units were damaged by the flames, and two units below them received significant water damage as crews worked to stop the blaze.

No people were injured in the fire, officials confirmed, although a dog in one of the apartments was found dead. 

After both the ceiling and the floor of one of the apartments collapsed, one firefighter fell partially through the destroyed floor but was able to pull himself up without injury. 

After the collapse, the fire was declared a defensive fire and all firefighters were able to safely exit.

The displaced residents were being assisted by the Phoenix Crisis Response Team. 

Investigators are working to determine the cause of the fire. 

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