Baltimore City Fire Department spokesman Kevin Cartwright said 10 people were in the home and five had escaped by the time crews arrived, WBAL-TV, Baltimore, reported.
Cartwright said a grandmother and four children had died.
Fire investigators were trying to determine the cause of the blaze they said they think it originated in the basement, WMAR-TV, Baltimore, reported.
Firefighters were met with heavy flames and smoke from the first floor through the second floor when they arrived, WBAL said.
"To explain just how intense this fire was, there was an adult male who jumped from the second floor window to escape the flames," Cartwright said.
A firefighter was injured when he fell from the second floor to the basement, WMAR-TV said.
The man injured when he jumped from from the window was taken to an area hospital.
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