PHILADELPHIA (AP) — Fire tore through a duplex home early Wednesday in Philadelphia, killing 13 people, including seven children, fire officials said. At least two people were sent to hospitals, and officials warned the toll could grow as firefighters searched the rowhome, where 26 people had been staying.

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.

“I can’t picture how more people couldn’t get out — jumping out a window,” she said.

City and fire officials did not release the names or ages of those killed in the blaze, which started before 6:30 a.m. in a residential area of the city’s Fairmount neighborhood, northwest of downtown and home to the Philadelphia Museum of Art and its famous “Rocky steps.”

Relatives and friends of the home’s residents gathered at a nearby elementary school to wait for news, some wrapped in Salvation Army blankets, The Philadelphia Inquirer reported. Several friends of the children stopped by, hoping for information, after their texts and calls went unanswered.

“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.

“Losing so many kids is just devastating,” said Mayor Jim Kenney. “Keep these babies in your prayers.”

First lady Jill Biden, who along with President Joe Biden has deep ties to the Philadelphia area, tweeted, “My heart is with the families and loved ones of the victims of the tragic fire in Philadelphia.”

Crews responded around 6:40 a.m. and saw flames shooting from the second-floor front windows in an area believed to be a kitchen, Murphy said. The odd configuration of the building — originally a single-family home that had been split into two apartments — made it difficult to navigate, he said. Crews brought it under control in less than an hour, he said.

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.

Murphy noted that 26 was a large number of people to be occupying a duplex, but a spokesperson for Philadelphia’s Department of Licenses and Inspections said the city does not limit the number of family members who can stay in a single unit. And the mayor said people should withhold judgment.

“You don’t know the circumstances of each and every family, and maybe there were relatives and family that needed to be sheltered,” Kenney said. “Obviously the tragedy happened, and we all mourn for it. But we can’t make judgment on the number of people living in the house because sometimes people just need to be indoors.”

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, adding that the last inspection was in May 2021.

“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.”