An NYPD officer shot and killed a man in his Brooklyn apartment after the man allegedly came at them with a knife, police said Monday.

"I heard the gun like plah, plah, plah, like four shots I heard and that was it," said one woman outside the building. "Next thing I see it's a bunch of police on the floor."

An officer fatally shot Dwayne Jeune, 32, inside the Flatbush Gardens complex, according to police.

NYPD Chief of Patrol Terence Monahan said it occurred just after 12:20 p.m.

They said four officers responded after Jeune's mother called police and told them he was emotionally disturbed and needed help.

Officials said she told 911 that Jeune was not violent and was not armed.

Police said Jeune charged at the officers with a large carving knife, seen below.

According to Monahan, one of the officers tasered the man but was unable to disable him.

Police said a second officer then shot Jeune in the chest. He was pronounced dead at the scene.

Advocates and neighbors questioned if police did enough to de-escalate the situation.

"She wasn't calling to be able to say, 'Hey, my son is attacking me,' but he had some challenges and having an episode, and she was calling to be able to get help, not to have her son be dead," said Rev. Kevin McCall of the National Action Network.

"He was a very cool guy," one neighbor said. "He was a little mentally disturbed and stuff like that, but he wasn't a threat"

"He never bothered nobody, say nothing to nobody, he always said, 'Hi,' walking by, doing regular stuff," another neighbor reflected. "Come on, man, they are killing anything now. Now they just want to kill anybody."

"What's the protocol? Was it followed? Why wasn't it followed," Brooklyn City Councilman Jumaane Williams told reporters.

Mayor Bill de Blasio acknowledged those questions Monday in his weekly NY1 interview, "Mondays with the Mayor," while saying police have to judge the risks in situations like this.

"This happen very quickly, where officer are in immediate danger, or someone else might be — a civilian or a family member might be in immediate danger," de Blasio told NY1's Errol Louis. "So we have to get all those facts."

Jeune's 14-year-old neighbor, Lasaunti Newell, showed NY1 a hole from the stray bullet that she says put her in danger.

"I woke up to the sound of the gunshot like flying through the walls," Newell said.

"It's really devastating to me knowing what could have happened to her," Newell's mother told reporters.

"You could have shot him in the leg or the arm," she added about the shooting.

The investigation is ongoing.