NEW YORK (AP) — A 93-year-old New York City woman died, and another was rescued, when fire and smoke filled a building. Firefighters said one focus of the investigation is on an e-bike battery that might have exploded into flames.

If so, it would add to the mounting number of deaths city officials blame on malfunctioning e-bike batteries.

With some 65,000 e-bikes zipping through its streets, New York City is the epicenter of battery-related fires. There have been more than 100 such blazes so far this year, resulting in at least 14 deaths, already more than double the six fatalities last year.

Fire officials said the elderly victim, Kam Mei Koo, was found unconscious on the second floor. She was pronounced dead at a nearby hospital.

Jack Koo, who identified himself to the New York Daily News as the woman’s son, said he had left the building earlier in the day, only to return to see the fire-gutted building and learn of his mother’s fate.

“I left to pick up my daughter and I came back to this,” Koo told the paper. “My mother is dead. What can I do? What can I do?”

The fire and smoke had spread quickly, according to Marie Rodriguez who made a harrowing escape.

“I was taking a nap and I heard something pop three times real loud,” Rodriguez told WABC. “Woke up, then I started choking. And when I looked to the door, I saw smoke coming in.”

She ran to the window as she gasped for air. She leaned outside the window as onlookers urged her to jump then tried to rescue her with a ladder.

But firefighters soon arrived and rescued her.

The Daily News reported that Koo, the dead woman’s son, told fire officials that the bike was his.