New York City’s beleaguered housing projects are as bloody as they are broken.

While the city enjoys a 4% decrease in serious crime so far this year, NYC Housing Authority complexes saw a 5% increase in the seven index crimes, according to NYPD data through Sept. 1.

Murders surged 17% compared to the same period last year, and shootings were up 13%. Citywide, murders were down 4%, and shootings up 8%.

The 22-building Wagner Houses in East Harlem has become a battleground for gangbangers, with a 15% overall crime increase. It was the only NYCHA complex in the Top 5 in each of the four violent-crime categories — murder, rape, robbery and assault — according to a Post analysis of the Compstat data.

An 80-year-old resident, Julia Jenkins, lives with the violence. On July 15, at about 1 a.m., gunshots whizzed past her apartment, killing 28-year-old Terrence Santos. A second, 27-year-old victim survived the shooting. Both were members of the “FlowBoyz,” a police source told The Post. The gang has operated out of Wagner for years.

“I heard what I thought were firecrackers and looked out my window and saw him on the ground,” the 50-year resident of the Wagner Houses recalled. “Then I heard a lady say, ‘You didn’t have to shoot him.’ ”

The killer is still at large.

Ironically, the 4,800-tenant development served as a backdrop for Mayor de Blasio’s 2014 announcement that City Hall would pour $210 million into making NYCHA safer. That same year, the NYPD deployed an additional 700 cops to 15 crime-ridden projects.

In another attempt to crack down on crime at Wagner, the NYPD arrested about a dozen members of the Wagner-based “Chico Gang” in February. Police say the group is responsible for 17 shootings from November 2015 through January 2019.

But Wagner residents say police presence has dwindled since.

“They need to see more cops present, not just passing by,” said a resident who has lived at Wagner since it opened in 1958. “They used to have them in the buildings more. Now you only see them when there’s an altercation.”

The resident said gang activity seemed to reach a fever-pitch this summer.

“In 64 years I’ve seen a whole lot, and this is the worst it’s ever been,” he said. “When the weekend comes, you can feel the tension. There are broken bottles all over the place. The crowds get a bit younger. It’s just so out of hand.”

Across the East River from the Wagner Houses, the sprawling Queensbrige complex was the scene of 40 violent crimes during the first eight months of the year — more than any other NYCHA complex. It’s the city’s largest project.

The NYPD hopes the trend began to turn in the first week of September, when NYCHA index crimes were down 13% compared to the same seven days in 2018.

“The [housing police] commanding officer is aware of the crime conditions within the development and is working to address them,” NYPD spokeswoman Sgt. Jessica McRorie said. “Year-to-date, as of Sunday Sept. 8, there is a decrease in burglaries, and there is no increase in rapes or robberies” at Wagner.

McRorie said the NYPD has made arrests in eight of the nine robberies at Wagner and in 16 of the assault cases, which increased to 25 in the first week of September.