Here’s what happens when Mayor Bill de Blasio and the NYPD turn a blind eye to illegal fireworks on city streets — a bloody start to the Fourth of July holiday.

The wild incident that left five people stabbed erupted at around 1:22 a.m. Friday at St. Mary’s Park in The Bronx when a man started shooting off fireworks, police said.

The man, 24, blasted one too close to a group of men inside the green space — either deliberately or by accident — sparking an argument that turned bloody, cops said.

Police say the 24-year-old man is believed to have then stabbed four men — a 21-year-old in the back, a 19-year-old in the right arm, a man in his 20s in the face and right leg and a 22-year-old in the right side of his head — during the melee.

One of the men who was stabbed then turned the knife on the fireworks shooter, slashing him in the chest, according to cops.

The five men were taken to Lincoln Medical Center and all were expected to survive. No arrests have been made.

Neighbors say that for weeks, there have been large gatherings — including one of around 700 people — at the park at night where people play music, drink, smoke “reefers” and set off fireworks.

“Every morning, every evening, every night — all hours of the day. It’s a constant,” one neighbor said of the fireworks activity.

The early Friday commotion awoke a longtime area resident who would only identify himself as Ellis.

“These guys went across the street and they started swinging at one of the two people sitting down,” said Ellis, who claimed he has called 311 in the past about the activity in the park at night.

“We are afraid — it might burn our properties down,” he said. “They ignite the firecrackers and they go up over the houses.”

Asked why the mayor continues refusing to ticket or arrest people for blowing off fireworks — especially given the ongoing risk to public safety —  a City Hall spokeswoman said that the incident was being investigated, and that the Fireworks Task Force has enforcement discretion.

The task force is comprised of FDNY Fire Marshals and officers from the NYPD Intelligence Bureau and Sheriff’s Bureau of Criminal Investigation.

The bloody fireworks fight comes after weeks of a hands-off approach by the city and police to stop skyrocketing illegal fireworks activity on Big Apple streets – and after Brooklyn Borough President Eric Adams advised New Yorkers to take matters into their own hands instead of calling 311 or 911 on those shooting off fireworks.

Adams’ spokesman Jonah Allon said that the BP “stressed that 911 should not always be the first call people make” and that: “In this case, someone appeared to have been using the fireworks in a dangerous and disorderly manner, which would make it appropriate to contact the proper authorities. We don’t want people taking dangerous law enforcement actions into their own hands.”

Neighbors should “go talk to the young people or the people on your block who are using fireworks” and warn them of the dangers, Adams said in June.

In addition to the fireworks stabbing fracas, there were five shootings with six victims — all of whom were expected to survive — and a domestic stabbing in a Queens home that left a woman dead during an overnight crime spate in the city.

Cops were called to the Jackson Heights, Queens home at 34th Road around 2:19 a.m. for a report of an assault and found a 45-year-old Yaqueline Collado with multiple stab wounds and her 41-year-old husband with stab wounds to his abdomen, authorities said.

The husband, whose identity was not immediately released, remains in critical condition and in police custody.

In the last week, there have been 34 shooting incidents with 43 victims, compared to 26 shooting incidents for the same week last year, police sources said.

Additionally, there were eight murders during that time frame, compared to 12 in the same time period last year, according to sources.

Additional reporting by Tina Moore