A little before 7pm (midnight GMT/6am BdST) on Thursday, the child, who had been left unattended in the kitchen, started screaming as it filled with smoke and fire, Daniel Nigro, the city's fire department commissioner, told reporters at a news conference.
By the time the boy's mother was alerted to the fire, officials say the flames had spread too far.
Currently, there are four individuals in critical condition that are fighting for their lives in the hospital. "It felt like we'd been living in a war zone", said Carole Van Duzer of Erie, Pennsylvania, which was buried this week under five feet of snow.
"When I saw it on the news this morning I started crying", said Nancy Clark, a 42-year-old Bronx resident, who came to the scene Friday to donate blankets, phone chargers and toiletries to the families who had been displaced.
Excluding the September 11 attacks, it was the worst fire in the city since 87 people were killed at a social club fire in the Bronx in 1990. Excluding the September 11 attacks, it was the worst fire in the city since 87 people were killed at a social club fire in the Bronx in 1990.
The fire spread up the stairs and cut off exit points for people on the upper floors.
Some tenants of the building, a mix of native New Yorkers and Latino and African immigrants, climbed down fire escapes.
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A National Guard soldier who was home for the holidays died while saving people from the massive apartment fire in the Bronx borough in New York City on Thursday night, according to several news reports.
Those who died Thursday night included girls ages 1, 2 and 7, and a boy whose age was not given.
Batiz wrote on a Go Fund Me page that her mother, Maria Batiz, 57, called her at work to tell her that a fire had broken out in the building and she and the baby were trapped. "God rest their souls, they're lovely". He added that it's not unusual for children to be fascinated by fire or rare for children to start them.
According to city records, the building had no elevator.
Rajkumar Ramdhani, who lived with his wife on the second floor of the building, said two grandchildren were visiting from Virginia when the fire broke out.
In 2007, 10 people - nine of them children - were killed in fire at a Bronx residence after a space heater cord overheated. "But when you have this number of people pass as a result of a disaster like this, it's heartbreaking", de Vulpillieres said. No one has been able find Mensah; his family has checked four hospitals.
"It seems like a terrible, tragic accident", Mayor Bill de Blasio said in an interview with WNYC radio.