Jacuita Purifoy lost ten family members when a fire tore through a converted three-storey house in Philadelphia Wednesday, killing 12 people in one of the United States' deadliest residential infernos in recent years.

"My sisters and my nephews and my nieces are gone. They are never coming back again," the 37-year-old told AFP outside a nearby elementary school where families of victims were consoling each other.

Eight children were killed in the blaze. Purifoy lost seven younger relatives, the youngest of whom was just one year old. 

Three of Purifoy's sisters also died in the fire, which happened just before sunrise in public housing in the eastern US city's popular museum district of Fairmount.

"I am in shock. I don't know what to do. I don't know what to say," said Purifoy. "They were somebody who was supposed to continue life and die of old age, not from stuff that could have been avoided."

Officials said eight people escaped the flames, while another two were hospitalized. One of the two receiving treatment was a five-year-old nephew of Purifoy.

"Everybody is gone except for one child," she said.

"He doesn't know what's going on. He wants his mom, he wants his dad, he wants his sisters, he wants his cousins, he wants everybody that he had lived with for the past five years.

"He doesn't know what's going on, because he's still a child," Purifoy added.

At the Bache-Martin Elementary School, a block away from the site of the disaster, a Salvation Army truck handed out supplies to relatives.

Purifoy rubbed the back of her sister Qaadira, who wept as she tried to keep out the cold with a Salvation Army blanket.

Near the burnt building, a local laid a white rose on the ground under police tape.

- Investigation -

"This is without a doubt one of the most tragic days in our city's history, the loss of so many people in such a tragic way," Mayor Jim Kenney told reporters earlier Wednesday.

Philadelphia Fire Department deputy commissioner Craig Murphy said the fire was the worst he had seen in 35 years on the job.

He added it was too early to say what caused the blaze, but that his department was investigating.

"It's not necessarily considered suspicious, but we have all hands on deck because of the magnitude of this fire," he told reporters.

"We're in the process of investigating this to the highest level that we can. We're incorporating all of our resources."

He said that there were four smoke detectors in the building, but none of them had been operating.

The building is owned by Philadelphia's public housing authority (PHA), which said the detectors had last been inspected in May 2021 and "were operating properly at that time."

"This unimaginable loss of life has shaken all of us at PHA," CEO Kelvin Jeremiah said in a statement.

Officers found "heavy fire" coming from the second floor of the three-story row house when they arrived at 6:40 am (1140 GMT), and took almost one hour to get it under control, the fire department said in a tweet.

About 26 people had been living in the building, eight on the first floor and 18 across the second and third floors, according to Murphy.

- 'Tragedy' -

It wasn't clear how many people were in the building during the fire.

"Obviously the tragedy happened and we all mourn for it. But we can't make judgment on the number of people in the house," said Kenney.

The Philadelphia Inquirer quoted police as saying that the three-story home had been converted into two apartments.

The residential area is just a few blocks' walk from the Philadelphia Museum of Art and the Rodin Museum.

"It's a great tragedy for our neighborhood," Ruslan Boroviy, a priest at the nearby Saint Nicolas Ukrainian Catholic Church, told AFP.

The death toll was almost double that of a fire in Philadelphia in 2008, when seven immigrants died after a kerosene heater exploded in a three-story brick complex.

In December 2017, 13 people were killed in a blaze in an apartment building in the Bronx, in New York City's deadliest fire in 25 years.

Purifoy, whose father died recently, said her family was always close.

"We were together regardless of the family functions. We always stayed together. We stuck together because we were a family," she said.