The fast-moving fire broke out just before 11 p.m. on the second floor of a three-story residential building at 165 Schaefer Street in Bushwick.
It was placed under control about an hour later.
Five people were found inside the apartment where the fire started.
The two children, Haley Harris, 8, and Payton Gomez, 7, were pronounced dead at Wyckoff Hospital.
The Medical Examiner will determine the cause of death.
Three adults were taken to the hospital with non-life-threatening injuries.
The building owner says the two girls were visiting their grandfather for the weekend.
#New They were just 7 and 8 years old, sisters spending the weekend with their grandfather. A #Fire broke out in their #Brooklyn apt, killing the girls. The building owner, who knew the girls since birth , was devastated #abc7ny #fdny @ABC7NY @FDNY pic.twitter.com/TD04r3va5r— Kemberly Richardson (@kemrichardson7) December 9, 2018
Investigators are trying to determine the cause of the fire.
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