Multiple individuals were seriously injured by smoke in a fire that killed 19 people, including nine children, in a Bronx apartment building on Monday, as hospitals struggled to save their lives.

After Sunday’s fire, which was already New York City’s worst in three decades, dozens of people were hospitalized, with up to 13 in serious condition.

The fire in the 19-story structure was caused by a defective electric space heater that had been plugged in to provide extra heat on a cold morning.

The flames only burned a tiny portion of the building, but smoke escaped through the open door of the apartment and billowed down the stairwells and corridors, trapping many people in their homes and rendering others unconscious as they left.

After being brought out, many limp toddlers were spotted being given oxygen. Soot coated the faces of the evacuees.

According to Fire Commissioner Daniel Nigro, firefighters discovered fatalities on every story, many of whom were in cardiac and respiratory arrest. He claimed that several people were unable to flee due to the volume of smoke.

Even when their oxygen supply ran out, firefighters continued to make rescues, according to Mayor Eric Adams.

“Even though their oxygen tanks were empty, they pushed through the haze,” Adams explained.

An investigation is ongoing, according to Fire Commissioner Daniel Nigro, to investigate how the fire spread and whether anything could have been done to prevent or control the flames.

Smoke alarms are installed in the building, however some tenants claim they were first disregarded because alarms were so ubiquitous in the 120-unit building.

New apartment buildings in the city are obliged to have sprinkler systems and inside doors that swing shut automatically to limit smoke and deprive flames of oxygen, but thousands of older structures are exempt from these requirements.

Stairwells – the sole means of escape in a structure too tall for fire escapes — became gloomy, ash-choked monsters as a result of the smoke.

When Sandra Clayton saw the hallway fill with smoke and heard people yelling, “Get out!” she grabbed her dog Mocha and escaped for her life. “Get the hell out of here!”

Clayton, 61, claimed she stumbled down a darkness stairwell while carrying Mocha. She couldn’t see since the smoke was so thick, but she could hear people sobbing and crying nearby.

Clayton said from a hospital where she was treated for smoke inhalation, “I simply rushed down the steps as fast as I could but people were falling all over me, screaming.”

Her dog escaped from her clutches during the excitement and was later discovered dead in the stairway.

Jose Henriquez, a Dominican immigrant who resides on the 10th floor, claimed the building’s fire alarms would go off regularly but would always be false.

“It appears that they went off today, but no one paid notice,” Henriquez stated in Spanish.

When he and his family realized the smoke in the halls would overwhelm them if they tried to exit, they wedged a damp towel beneath the door.

Luis Rosa claimed he originally mistook it for a false alarm as well. The smoke was so heavy that he couldn’t see down the hallway as he opened the door to his 13th-floor flat. “So I replied, OK, we can’t race down the stairs because we’ll end up suffocating if we run down the stairs.”

He explained, “All we could do was wait.”

The fire was the deadliest in New York City since an arson at the Happy Land social club in the Bronx killed 87 people in 1990. A devastating apartment building fire in 2017 killed 13 people, and a fire in 2007 killed nine people, both of which were sparked by a space heater.