(CNN)New York City and Philadelphia are both mourning the loss of dozens of lives lost, including many children, in horrific apartment housing fires over the past few days.
Together, the two fires killed 31 people, 17 of them reportedly children.
Adding to the tragedy are the winter temperatures in the region and the raging Covid-19 pandemic, which is straining healthcare systems almost everywhere.
The fire in Philadelphia's Fairmont area
Early Wednesday morning, a fire ripped through a crowded apartment building in Philadelphia, killing at least 12 people, most of them children.
The victims included three sisters and all but one of their 10 children, a family member told CNN.
Rosalee McDonald, 33; Virginia Thomas, 30, and Quinsha White, 18, were killed, according to their cousins Frank and Pamela McDonald. Six of Rosalee McDonald's children and three of Thomas' children also died in the fire. The ages of their children were not given.
"They were both good people, good mothers and were very family-oriented," Frank McDonald told CNN. "Rosalee was one of the best people you could ever meet. She was very supportive -- they both were. They came down to help me with my business when I opened it."
The building was a three-story home converted into apartments that housed 26 people, according to fire officials.
Bill Richards, who said he's lived on the block for 24 years, told CNN affiliate WPVI that before he knew of the fire, he heard a woman yell, "Oh, my God! Oh, my God!" He then heard fire trucks and went outside.
Neighbors and others -- some sobbing -- gathered outside as firefighters and police worked the scene Wednesday morning, WPVI reported.
A veteran firefighter called it one of the worst he'd ever confronted.
"It was terrible," Philadelphia Deputy Fire Commissioner Craig Murphy said. "I've been around for 30, 35 years now, and this is probably one of the worst fires I've ever been to."
"This is without a doubt one of the most tragic days in our city's history -- loss of so many people in such a tragic way," Mayor Jim Kenney said Wednesday morning. "Losing so many kids is just devastating. ... Keep these babies in your prayers."
The cause of the fire is under investigation. One possibility being pursued is whether a child under the age of 5 playing with a lighter under a Christmas tree could have sparked the blaze, according to Jane Roh, spokesperson for the Philadelphia District Attorney's office.
The Bronx fire
In the Bronx in New York, 19 people, including nine children, died in a five-alarm fire that roared through an apartment building on Sunday.
Of the 63 people injured, 32 were hospitalized with life-threatening conditions, Fire Department New York Commissioner Daniel Nigro said.
The fire started in a malfunctioning space heater in an apartment that spanned two floors, according to Nigro. It consumed that apartment, Nigro said, and then smoke overwhelmed the staircase and people trying to get out.
"The door to that apartment -- unfortunately when the residents left -- was left open; it did not close by itself. The smoke spread throughout the building, thus the tremendous loss of life and people fighting for their lives right now in hospitals all over the Bronx," Nigro said.
There were no fire escapes on the building. About 200 firefighters responded to the blaze, and some them ran out of oxygen as they tried to get residents out, Nigro said.
Daisy Mitchell, who lived on the 10th floor, told CNN affiliate WABC she was really scared leaving her apartment.
"I just hear people banging on doors saying 'it's a fire, it's a fire,' so I ain't pay it no mind, but then when we opened that door the smoke just hit us, and we ran to the hallway to the exit and I just panicked, I got scared, even with the mask on," Mitchell told CNN affiliate WABC.
Mamadou Wague, who lived in the apartment where the fire started, told WABC he leapt through flames to save his daughter.
"We was sleeping and then my kids were screaming saying fire, fire," Wague said, according to WABC.
"I don't want to hear anybody dead in this fire, that's what I worry about," Wague told WABC.
The blaze is "going to be one of the worst fires that we have witnessed during modern times here in the city of New York," New York Mayor Eric Adams said.
"This is a horrific, horrific, painful moment for the city of New York, and the impact of this fire is going to really bring a level of just pain and despair in our city," Adams said.
CNN's Elizabeth Joseph, Amir Vera, Laura James, Eric Levenson, Alaa Elassar, Laura Studley, Mark Morales, Laura Dolan, Carll Alvarado, Paul P. Murphy and Taylor Romine contributed to this report.