A fast-moving fire early Wednesday morning in an overcrowded Philadelphia Housing Authority property caused a staggering number of fatalities and led to probing questions about the state of the building.

The blaze was reported at around 6 a.m. at a three-story duplex on the 800 block of 23rd Street in the Fairmount neighborhood, but by the time firefighters got it under control at 7:30 a.m., 12 people had died, eight of them children, city officials confirmed. The first-floor unit reportedly had eight people living in it at the time, while the unit split between the second and third floors had 18. Eight people made it out of the building alive.

“It was terrible," Philadelphia Deputy Fire Commissioner Craig Murphy said during a press conference, CBS 3 reports. "I’ve been around for 30, 35 years now and this is probably one of the worst fires I’ve ever been to.”

Standing at the scene in the late morning, Mayor Jim Kenney asked people not to pass judgment on the duplex's housing situation, raising the possibility that some of the people inside were visiting for the holidays or had been displaced from other housing situations, CBS 3 reports.

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

On the day of the fire, there were no working smoke or carbon monoxide detectors in the building, ABC 6 reports. When the two units were last inspected in the middle of last year, seven smoke detectors and three carbon monoxide detectors were working in the first-floor unit, while six smoke detectors and three carbon monoxide detectors were working in the other unit, PHA President and CEO Kelvin Jeremiah said in a statement. PHA declined to comment beyond the statement when contacted by Bisnow.

“This unimaginable loss of life has shaken all of us at PHA," Jeremiah's statement read in part. "It is too early for us to say more ... The Fire Department, [the Bureau of] Alcohol, Tobacco and Firearms and others are handling the investigation. Any information on the cause will come through them. Our primary goal right now is to support our residents in any way we can.”

The building's front and rear doors were the only means of exit, fire department officials said, describing the layout of the duplex as unusual, CBS 3 reports. Neighborhood residents at the scene said they had alerted PHA to the lack of escape routes from the building years ago.

The property did not have any active violations or investigations from the Department of Licenses & Inspections, WHYY reports. PHA Vice President of Operations Dinesh Indala told CBS 3 that the authority was not aware that 26 people were living in the property.

PHA, which was formed by the commonwealth of Pennsylvania, is the fourth-largest public housing authority in the U.S., and the duplex that caught fire was one of many "scattered sites," as PHA terminology describes them, the authority owns and rents to those with demonstrated need.

UPDATE, JAN. 6, 9:15 A.M. ET: This article and its headline have been updated to reflect the fire's confirmed casualty count from the mayor's office.