A Metro-North train loaded with holiday travelers derailed as it hurtled around a tight Bronx curve just north of Manhattan on Sunday — leaving at least four dead and 63 injured in a crash the engineer blamed on brake malfunction.

“It was just a bloodbath,” a shaken FDNY worker said of the scene of twisted metal and shattered glass along a bucolic stretch of the Hudson River, where the accident occurred just north of the Spuyten Duyvil station at 7:22 a.m.

Rescue crews were still working early Monday morning to right three of the seven derailed passenger cars to look for more possible bodies.

The train’s operator — 20-year MTA veteran William Rockefeller, 46, of upstate Germantown — was said to have told emergency responders that the brakes didn’t work.

“The guy’s distraught over the accident and the people who were injured,” a source said of Rockefeller, who was among those hurt.

All of those killed were New Yorkers. They included two women — Ahn Kisook, 35, of Queens, and Donna Smith, 54, of Newburgh — as well as married dads James Ferrari, 59, of Montrose and James Lovell, 58, of Cold Spring.

Three of the dead were thrown from the Hudson Line train, which had originated in Poughkeepsie at 5:54 a.m., bound for Grand Central. Their bodies were recovered between the second and third cars.

Passenger Emilie Miyauchi, 28, said she used her yoga mat to cover one of the victims.

“[She] seemed like she had lost most of her head. The side of the car was just covered in her blood,” she recalled.

It was the first time any passenger had been killed in Metro-North’s 31-year history.

Riders described chaos as the train flew off the tracks.

“I was just holding on . . . and people were flying around,” said Eddie Russell, 48, who was headed to work as a guard at SiriusXM. “I was afraid I was going to fall out the window.”

Joel Zaritsky said he was asleep and woke up as his train car started rolling over.

“Then I saw the gravel coming at me, and I heard people screaming,” he said.

The scene “looked like a toy train set that was mangled by some super-powerful force,” Gov. Cuomo later told CNN.

Gov. Cuomo said Monday that the high speed of the train probably caused the accident.

“I think it’s going to be speed-related,” he said. “It’s not about the turn. I think it’s going to be about the speed…” he said on NBC’s “Today” show.

Cuomo added that investigators are still trying to determine if the excessive speed was caused by “operator error” or a mechanical or other problem.

The governor called the scene of the tragedy horrific.

“It was actually worse than it looks,” he said.

Later, on Fox’s “Good Day New York,” he said it was hard to describe what he saw.

“This was breathtaking,” Cuomo recalled. “One minute everything is fine and the next minute we lost New Yorkers in a really tragic and violent way.

The first train car landed inches from Spuyten Duyvil Creek. NYPD divers searched the water to make sure no victims were thrown in.

The train, pushed by a diesel locomotive from behind, should have been going 70 mph before it slowed to 30 mph to round the curve, officials said.

Passengers told probers that the train seemed to be going much faster than usual.

“I have no idea why. I take this train every morning, and they always slow on this curve,” passenger Frank Tatulli told WABC-TV.

Investigators recovered the train’s “black box,” which should reveal how fast it was going when it crashed, said officials with the National Transportation Safety Board, which is leading the probe.

There were 120 passengers aboard — making it about half full — along with four crew.

At least 11 people were critically hurt, including a man in his early 40s who suffered a spinal-cord injury and may be paralyzed, authorities said. A 14-year-old boy also was critical.

Another six people were hospitalized in serious condition.

The train’s conductor was among those injured, as were three city cops. The most seriously hurt officer, Elsie Rodriguez, was on her way to work at her domestic-violence post at the 40th Precinct station in The Bronx, said sources, who added that she broke her collarbone.

Police Commissioner Ray Kelly visited Rodriguez at St. Barnabas Hospital in The Bronx. Mayor Bloomberg — who had been MIA for most of the day, with staffers refusing to say where he was — also dropped in to see Rodriguez on Sunday evening.

“We chitchatted about her job and how I was going to be unemployed, and she thought that was funny,” Bloomberg said.

Asked about why he hadn’t been at the accident scene, the mayor responded, “What can I do? I’m not a professional firefighter or a police officer. There’s nothing I can do! What I can do is make sure the right people from New York . . . are there and have all the resources that they want.”

Two other cops were treated at Montefiore Medical Center, also in The Bronx. They were identified as Richie Hernandez of the NYPD’s Special Victims Unit and Gabriel Rodriguez of the 42nd Precinct. Rodriguez, who was on his way to work, was treated for a leg injury and released, sources said.

An NYPD school-safety officer also was on board, along with a Police Department recruit, but neither was hurt, sources said.

NTSB member Earl Weener said six teams of investigators would be probing everything from the train’s speed and instruments to its maintenance and personnel records and the condition of the tracks.

“Our mission is to understand not just what happened but why it happened,” he said.

Cuomo insisted that the train route’s curve had nothing to do with anything.

“Trains take the curve every day 365 days a year, so it’s not the fact that there’s a curve here,’’ he said. “There has to be another factor.’’

The accident was the second involving a Metro-North train in six months.

Additional reporting by Kate Sheehy, Reuven Fenton, David K. Li,Elizabeth Hagen, Amanda Lozada and Rebecca Harshbarger