Underneath the N and W lines early Monday morning in Astoria, at least three people called 911 reporting a man acting erratically and wielding a knife — some worried he might stab someone.

Police said officers arrived in minutes and followed the man across 30th Avenue while ordering him to drop the knife.

“So as you can imagine, it’s fast moving. It’s hectic,” said NYPD Chief of Department John Chell. “Drop the knife, drop the knife.”

The knife was 14-inches long. Police said they unsuccessfully tried to subdue the suspect with tasers. When the man began moving towards an officer, police said a cop opened fire.

“Trying to keep out space, trying to keep him contained, but like I said at some point, he advanced toward our officers and we have to defend ourselves,” Chell said.

Officers tried to help the 61-year-old man until the ambulance arrived, but they were unable to save him.

Andre Johnson, a manager at the Trade Fair supermarket located on the corner where the incident took place, said he heard the gunshots.

“Loud firecrackers,” he said. “A loud noise.”

The incident happened under the 30th avenue N and W station on 31st street.

“It’s such a busy area for pedestrians,” said Angela Leising, who lives in the neighborhood. “I take my daughters every single day through that same intersection. There’s commuters, there’s kids, there’s several schools in the nearby area.”

Leising said she walks through the intersection near 30th Avenue and 31st Street at least four times a day and worries about police using lethal force.

”A potential bystander getting hurt or killed or injured,” she said. “And it’s a really tragic outcome for the person who was emotionally disturbed. I think that the police department can do better.”

Other Astoria residents believe officers were faced with a tough choice.

“Since the guy made a move carrying the knife towards the police, while they tell him to stop, I guess they had to do what they had to do,” Nicholas Giaoonatsis said.

When asked how many bullets were fired at the suspect, NYPD brass declined to give an exact number, while insisting that the goal in these types of situations is always de-escalation.

“The NYPD tried at all times to de-escalate and slow down these situations. Sometimes when you’re dealing with an armed person, you can see here a 14-inch knife. We are forced to defend ourselves,” Chell said.

NYPD officials said the man had two prior incidents of mental distress that the NYPD responded to, but would not elaborate on the details of those incidents.