The fire is on North 23rd Street in Philadelphia.
Two others, including one child, were critically injured and have been transported to hospitals. At least eight people were able to self-evacuate.
“It was terrible,” Deputy Fire Commissioner Craig Murphy said during a news conference. “I’ve been around for 35 years now, and this was probably one of the worst fires I’ve ever been to.”
The fire has been extinguished, but there is still an ongoing recovery effort, including a thorough investigation.
“This is without a doubt one of the most tragic days in our city’s history,” Mayor Jim Kenney said during the press conference. “Losing so many kids is just devastating.”
The fire started in the second story of a three-story row house, according to the department, around a kitchen.
Roughly 26 people lived in the building, which was divided into two duplex units. Eight people lived in the first and second floor unit, and 18 people lived in the second and third floor unit, which Murphy said was a “tremendous amount of people to be living in a duplex.”
Fire officials arrived on the scene of the fire just before 6:40 a.m. and said the fire was under control 50 minutes later.
The building was operated by the Philadelphia Housing Authority.
There were four batter operated smoke detectors in the building, none of which were working. An inspection was made in 2019 to install four smoke detectors, and the latest inspection was made in 2020, when two more smoke detectors were installed.
“Preliminary information indicates companies arrived at 6:40 a.m. and found heavy fire coming from the second floor of a three-story rowhouse,” the Philadelphia Fire Department tweeted earlier Wednesday. “It took 50 minutes to place the fire under control.”
This is a developing story. Check back for updates.
ABC News’ Aaron Katersky contributed to this report.