The fire at 665 New York Avenue in Flatbush was first reported around 10:30 a.m. and quickly escalated to 7 alarms.
The fire was ruled under control by 2 p.m. Authorities believe a lightning strike started the fire.
Fire started on the roof of the 7-story building. Officials said the roof was collapsing onto the floor below.
Firefighters are on the roof making a trench cut to get to the fire, authorities said.
More than 200 firefighters were on the scene, officials said.
The Fire Department said that there were a total of 52 injuries , but none of them were life-threatening.
Firefighters remained at the scene on Thursday night to go through debris.
The Red Cross says 120 families have been displaced and are being offered shelter at a nearby school.
Shondelle Rodney, said she rushed home from work when a friend called her saying the building was on fire. Her older sister was still asleep in the family's fifth-floor apartment.
"She didn't hear anything, so we called her," Rodney said.
The sister got out, taking along their dog and cat, she said, "but the bird is still up there."
The other residents of the apartment - another sister, their mother and two children - were not home when the fire started.
The family planned to spend the night at the school. Rodney didn't know when they'd be able to return.
The AP contributed to this report.
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