The four smoke alarms in the building, which was public housing, do not appear to have been working, fire officials said. The blaze's cause was not determined, but officials shaken by the death toll - apparently the highest in a single fire in the city in at least a century - vowed to get to the bottom of it.
"I knew some of those kids - I used to see them playing on the corner," said Dannie McGuire, 34, fighting back tears as she and Martin Burgert, 35, stood in the doorway of a home around the corner. They had lived there for a decade, she said, "and some of those kids have lived here as long as us."
"I can't picture how more people couldn't get out - jumping out a window," she said.
VIDEO: Chopper 6 over scene of fatal fire
City and fire officials did not release the names or ages of those killed in the blaze, which started before 6:30 a.m.
"It was terrible. I've been around for 35 years now and this is probably one of the worst fires I have ever been to," said Craig Murphy, first deputy fire commissioner, at a news conference near the scene later in the morning.
"Losing so many kids is just devastating," said Mayor Jim Kenney. "Keep these babies in your prayers."
Crews responded around 6:40 a.m. and saw flames shooting from the second-floor front windows of the home, in an area believed to be a kitchen, Murphy said. The odd configuration of the house, which had been split into two apartments, made it difficult to navigate, he said, but crews were able to bring it under control in less than an hour.
There were four smoke alarms in the building, Murphy said, none of which appeared to be working. There were 18 people staying in the upstairs apartment on the second and third floors, and eight staying in the downstairs apartment, which included the first floor and part of the second floor, he said.
The alarms had been inspected annually, and at least two had been replaced in 2020, with batteries replaced in the others at that time, Philadelphia Housing Authority officials said.
"It's just heartbreaking," said Andrea Duszenczuk, 68, whose family has long owned a home in the neighborhood and who walks her dog past the burnt home regularly. "A lot of these homes have old wiring - these are probably 125 years old. Who knows what's behind the walls."
Television news footage showed ladders propped up against the smoke-blackened front of the house, with all its windows missing. Holes remained in the roof where firefighters had broken through.