The blaze broke out around 9 a.m. in the 2100 block of Valentine Avenue in Fordham Heights.
Cell phone video from a neighborhood resident showed one home completely engulfed in flames.
The fire went to four alarms and spread to two adjacent homes before firefighters were able to bring it under control after about 90 minutes.
Kareem Parker lives in the apartment where the fire started.
"I knew it was too hot to go outside my room, and I had to hop out through the back," he said. "I was looking for anybody that was in there that I could try to save, but it was too hot."
His grandmother, 72-year-old Betty Lee, could not make it out. She was found dead in a rear bedroom.
"She was a good person in this community," he said. "She lived a long life."
Meantime, the family living upstairs from where the fire started said they had no choice but to jump from their second floor apartment to the porch roofs of the buildings on either side.
"No one could help us," said one displaced resident who didn't want to be identified. "There was no firefighters on site, there were no officers on site, There was just a lot of smoke coming in too quickly, and we had to get out as fast as possible."
Five other people, along with three firefighters, suffered injuries described as minor.
Residents of five homes in the Bronx were evacuated, including the initial fire building.
The cause of the fire remains under investigation.
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