(CNN) A fire tore through a 2nd-story Chicago home overnight, killing six children, two adults and a dog, the city's fire commissioner said.

"We have not had this in many, many, many years -- this amount of fatalities and injuries in one location," Commissioner José Santiago said Sunday morning.

But if not for the quick actions of a woman who smelled the fire, he said, the outcome could have been even more tragic.

The fire started on the 2nd floor of the building, Santiago said. The 1st floor of the building was vacant, and the 2nd floor was a home.

The relationships of those found on the 2nd floor was not immediately clear.

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