The Philadelphia Fire Department says eight children are among at least 12 dead.
A fire official said the number of fatalities is "dynamic," indicating the number of those killed could change as the recovery continues.
"Without a doubt one of the most tragic days in our city's history," Mayor Jim Kenney said at a news conference.
First lady Jill Biden tweeted, "My heart is with the families and loved ones of the victims of the tragic fire in Philadelphia."
My heart is with the families and loved ones of the victims of the tragic fire in Philadelphia.— Jill Biden (@FLOTUS) January 5, 2022
Gov. Tom Wolf said his "heart goes out to the loved ones left to cope with this heartbreaking loss of life."
Devastated over this morning’s tragic fire that killed 13 Pennsylvanians, including 7 children, in Philadelphia.— Governor Tom Wolf (@GovernorTomWolf) January 5, 2022
My heart goes out to the loved ones left to cope with this heartbreaking loss of life.
Thank you to the brave first responders who got the fire under control.
Archbishop Nelson Perez reacted to the heartbreaking news by extending "deep condolences to all those in mourning."
1/3 Dear Sisters and Brothers in Christ,— Archbishop Nelson Perez (@ArchbishopPerez) January 5, 2022
Like many of you, I have been following the heartbreaking local news this morning about a devastating house fire in the Fairmount section of Philadelphia that claimed more than a dozen lives.
In the name of the people of the @ArchPhilly, pic.twitter.com/jji0KS2h3R
Congressman Conor Lamb said he is praying "for the victims of the devastating fire" and their families.
Praying for the victims of the devastating fire in Philadelphia & all their loved ones. Grateful as always for the firefighters who work so hard to protect us. @IAFF22— Conor Lamb (@ConorLambPA) January 5, 2022
Rep. Malcolm Kenyatta expressed condolences for the victims.
I’m having a hard time finding the words to express my deep sorrow for the heartbreaking loss of 13 lives, including 7 kids, in this morning’s fire in Fairmount. This weighs heavy as we mourn those lost and keep hope for those being treated in the hospital.https://t.co/Myq74EiNtN— Rep. Malcolm Kenyatta (@malcolmkenyatta) January 5, 2022
Bill McSwain said his heart goes out to the families of this horrible tragedy - the whole City mourns with you.
My heart goes out to the families of the 13 victims of this horrible tragedy — the whole City mourns with you. Thank you to the brave first responders and @PhillyFireDept for their heroic actions to help quell this horrific fire. https://t.co/Jk5lot5vcF— Bill McSwain (@McSwainPA) January 5, 2022
Dr. Mehmet Oz said his heart breaks for the families who lost loved ones.
My heart breaks for the families who lost loved ones in the tragic fire in Philadelphia this morning. Thank you to the brave first responders on scene. https://t.co/RJP4dNDrNM— Dr. Mehmet Oz (@DrOz) January 5, 2022
Attorney General Josh Shapiro thanked first responders and offered his condolences.
Thank you to all the first responders and @PhillyFireDept for their brave actions at today’s deadly house fire in Philadelphia.— AG Josh Shapiro (@PAAttorneyGen) January 5, 2022
13 lives lost, 7 of them children. My thoughts are with the families impacted by this tremendous loss.