Philadelphia fire kills 13, including 7 children

(Philadelphia, PA) -- The Philadelphia Fire Department says 13 people, seven children included, are dead following a duplex fire in the Fairmount section of the city. 

"Without a doubt one of the most tragic days in our city's history," Mayor Jim Kenney said at a news conference. "Losing so many kids is just devastating... Keep these babies in your prayers."

Fire officials say there were no working smoke detectors in the home. 

The fire started around 6:40am. Firefighters arrived and found heavy flames coming from the second floor of the three-story home. Officials say 18 people lived in Unit B, the second and third floor of the duplex. Fire officials say most fatalities were from Unit B.

The Fire Department says an investigation is still ongoing into the cause of the fire, but suspect a Christmas tree fire may be the cause of the blaze.