A 4-year-old child is among 16 people injured in a fire inside a Sunset Park apartment building on Friday that's now under investigation, the FDNY said.

The fire began on the second floor of the three-story home on 45th Street near 6th Avenue just after 11 p.m., according to FDNY Assistant Chief of Fire Operations Michael Gala. The four-year-old child was found inside a second floor bedroom, Gala said.

"At the same time members found several victims on the top floor and removed them expeditiously from the fire building," Gala said. "We had a very high patient count."

The child is in cardiac arrest.

Sixty firefighters responded to the one-alarm fire, knocking out windows to extinguish the blaze that was brought under control just after midnight on Saturday. One witness told CBS 2 News they never witnessed a fire on their block.

“I smelled the smoke coming from my building and then by the time I came out, the trucks were already out there,” the witness said. “They were getting mattresses out and things like that from the house, and the kids were running down the block, actually […] I heard that people were jumping out to the backyard."

Four of the 16 victims suffered life-threatening injuries, with the rest having suffered from minor injuries, according to the FDNY. Some of the victims were transported to area hospitals by ambulance and NYPD officers, including the four-year-old child. No firefighters were injured.

Marshals are now investigating the cause of the fire.