Former NYPD Commissioner Bill Bratton says it is “mind-boggling” how much Texas authorities mishandled last week’s school massacre.

“I’ve never seen anything like it in all my years of policing,” Bratton said during an appearance on WABC 770’s “The Cats Roundtable” that aired Sunday. “I have so much anger at the moment at how mishandled this has been.”

Bratton — who has twice served as the Big Apple’s top cop — said he was stunned that local Texas cops waited so long to enter Robb Elementary School on Tuesday while 18-year-old Salvador Ramos was inside killing 19 fourth-graders and two teachers.

“To be hearing that some of those lives might have been saved. But a wrong decision was made apparently by a police chief with a six-person police force that was put in charge of the response to this horrendous incident,” he told radio host John Catsimatidis. “It’s mind-boggling and frustrating.”

Bratton, who also headed the Los Angeles and Boston police departments, said Texas authorities failed to adopt active-shooter guidelines that came about after the 1999 Columbine High School mass shooting in Colorado.

“We learned a lot … from the Columbine tragedy many years ago,” he said.

“Apparently, unfortunately, with how it seems to be shaping up, the officer in charge, the incident commander in this incident in Texas effectively after all the things we learned about this type of incident, he basically didn’t implement them,” Bratton went on. “He opted to keep those 19 officers outside the classroom.”

Meanwhile, “the misinformation that’s been put out by government officials in Texas is mind-blowing,” too, Bratton said.

Uvalde authorities have come under intense scrutiny for their handling of the massacre. Police did not enter Robb Elementary School for more than 90 minutes after arriving at the campus, where a deranged teenager fatally shot his innocent victims with an AR-15 assault rifle.

Bratton noted the hero off-duty Customs and Border Protection agent from an elite tactical unit who finally fatally shot the gunman.

“We now understand that there may have been an off-duty border patrol agent who is sitting in a barber shop. And his wife calls from the school. She’s a teacher, and she’s there with her daughter in the classroom,” he said. “He grabs a shotgun from the barber shop, rushes to the school, goes into the back of the school …  and rescues a classroom of children and his wife and his daughter, even as in another part of the school there are 19 police officers … in the hallways outside the classroom where the shooter is holed up.

“The children] were … dying literally, while the [police] were standing outside the door,” Bratton said. “How do you put your arms around this thing?”

His comments came as Texas state Sen. Roland Gutierrez revealed on CNN that the mother of one of the young massacre victims recalled to him how a first-responder told her the child might have lived if cops hadn’t been slow to move in on the killer.

During Bratton’s radio interview, he said his “pride” in his profession had been “diminished” by the police response in Texas.

“I have great pride in my profession, my former profession, policing. But that pride was diminished somewhat this week with the mishandling by the Texas authorities,” the retired chief told Catsmatidis.

“This has one of the most problematic weeks I’ve ever experienced in American policing in my 50 years.”

Bratton is not alone in his frustration.

On Friday, Texas Gov. Greg Abbott fumed that he was “livid” that law enforcement “misled” him about their response to the rampage at the elementary school. Abbott —  who earlier last week praised police for their “quick response” to the mass shooting — said initial information police provided to him about it was inaccurate, causing him to release misleading details to the public Wednesday. 

Ramos fired off at least 100 rounds and marched in through an unlocked building door that had been propped open by a teacher, authorities have said.

Police did not enter the classrooms until 78 minutes after the mass shooter with a history of violence toward women had walked inside.

Days after the shooting, police revealed the existence of a series of harrowing 911 calls from several students while they were barricaded inside with the gunman, with one kid begging a dispatcher, “Please send police now!”

The calls were taking place until moments before Ramos was killed, indicating that people were still alive in the class despite authorities believing the massacre had come to a halt.

A top law-enforcement official has said cops at the scene of the school shooting “made the wrong decision” when they waited to open the door of the class where Ramos was with the children.

That choice was made because the on-scene commander made the call that the carnage had gone from an active shooter situation to a “barricaded suspect” situation, Col. Steven McCraw, director of the Texas Department of Public Safety, said during a news conference.