At least 13 people are dead, including seven children, after a large house caught on fire in Philadelphia's Fairmount neighbourhood on Wednesday morning.
One child and one adult were taken to local hospitals, fire authorities said at a news conference. Eight people managed to escape the building.
Philadelphia Mayor Jim Kennedy told reporters to "keep those babies in your prayers", but did not provide their ages.
Deputy Fire Commissioner Craig Murphy added: "I've been around for 35 years now and this is probably one of the worst fires I've ever been to.
"I don't have the words for how we're feeling right now as a community and as a department."
The blaze occurred in a building owned by the Philadelphia Housing Authority, which had converted it into two apartments.
Twenty-six people lived in the terrace house, with 18 people living in the second unit alone.
"That is a tremendous amount of people to be living in a duplex," Mr Murphy said.
Authorities said none of the four smoke detectors in the building were functional.
Firefighters arrived at the three-story house at 6.40am local time and reported heavy fire coming from the second floor. It took 50 minutes to extinguish the blaze.
The origin and cause of the fire are currently under investigation.
The language of diplomacy in 1853
Treaty of Peace in Perpetuity Agreed Upon by the Chiefs of the Arabian Coast on Behalf of Themselves, Their Heirs and Successors Under the Mediation of the Resident of the Persian Gulf, 1853
(This treaty gave the region the name “Trucial States”.)
We, whose seals are hereunto affixed, Sheikh Sultan bin Suggar, Chief of Rassool-Kheimah, Sheikh Saeed bin Tahnoon, Chief of Aboo Dhebbee, Sheikh Saeed bin Buyte, Chief of Debay, Sheikh Hamid bin Rashed, Chief of Ejman, Sheikh Abdoola bin Rashed, Chief of Umm-ool-Keiweyn, having experienced for a series of years the benefits and advantages resulting from a maritime truce contracted amongst ourselves under the mediation of the Resident in the Persian Gulf and renewed from time to time up to the present period, and being fully impressed, therefore, with a sense of evil consequence formerly arising, from the prosecution of our feuds at sea, whereby our subjects and dependants were prevented from carrying on the pearl fishery in security, and were exposed to interruption and molestation when passing on their lawful occasions, accordingly, we, as aforesaid have determined, for ourselves, our heirs and successors, to conclude together a lasting and inviolable peace from this time forth in perpetuity.
Taken from Britain and Saudi Arabia, 1925-1939: the Imperial Oasis, by Clive Leatherdale
