A Bronx apartment building erupted in flames after a massive explosion Wednesday afternoon — with one killed and at least 14 people injured in the five-alarm blaze, the FDNY said.

Two people sustained life-threatening injuries and three firefighters were also seriously injured in the blast that rocked the third floor of the five-story apartment building at 374 E 209th Street around 12:30 p.m., according to the FDNY.

Officials said a blaze quickly broke out on the second and third floors of the building, and rapidly grew in little over an hour.

The scene of a five-alarm fire at 374 E. 209th St. in The Bronx on Wednesday, Aug. 5, 2026. Peter Gerber

At least two people were critically injured in the blaze. Peter Gerber

Sources told The Post that the building was no longer structurally sound as of Wednesday evening, and the third floor had already collapsed into the second.

The definitive cause of the collapse remains unknown, and authorities fear that the building may collapse further, sources said.

Four other people and three additional firefighters suffered minor injuries from the blast.

Some 300 FDNY firefighters and EMS responded to the scene, according to FDNY Commissioner Lillian Bonsignore.

“This was a very difficult fire on a hot and humid day,” Bonsignore said. 

An FDNY spokesperson said the emergency response will last “well into tomorrow.”

“As the commissioner said, there was some sort of explosion,” FDNY Chief of Department John M. Esposito said. 

“It blew out window frames. It blew some of them across the street. And when our members got up to the second floor, some of the apartment doors had been blown off the hinges as well.”

Lisa Landin said, who was commuting home from the bus said she heard a “crazy” explosion.

“It sounded like a bomb went off,” Landin said.

A grief-stricken woman who said her pets were stuck in the building when the explosion went off was just around the corner when the blast happened.

An explosion occurred in the third floor of the building around 12:30 p.m. on Wednesday afternoon. James Keivom for NY Post

FDNY firefighters spraying water at a window in the E 209th Street building. James Keivom for NY Post

Firefighters seen on the roof of the building and descending the fire escape. James Keivom for NY Post

“I was right around the corner. I saw the whole thing blow up in flames,” the tenant said.

“I didn’t know it was my building until one person ran to me and told me to get my dogs,” the grief-stricken woman recounted just outside the building.

“By the time I got here, they were already stopping people from coming in.”

The FDNY said that 18 people were displaced as a result of the fire. 

An investigation into the fire will take place as soon as it’s safe for fire marshals to investigate, officials said.

A resident, whose pets were stuck in the building, reacting to the Bronx fire. Peter Gerber