“He’s going to kill the baby!”

A pregnant real estate agent was dragged screaming from her Queens apartment and stabbed to death in the vestibule of her building early Sunday as she pleaded for the life of her unborn child, witnesses and police sources said.

The killer targeted the 35-year-old woman’s stomach, according to the building super, who said she watched surveillance video footage that captured the murder.

“He’s got a knife! He’s going to kill the baby!” shouted five-months-pregnant Jennifer Irigoyen around 1 a.m. as her attacker pulled her from her third-floor Ridgewood walk-up and down the stairs to the building’s entranceway, horrified witness Maurice Roman Zereoue told The Post.

Police are investigating the slaying as a domestic incident and seeking Irigoyen’s boyfriend for questioning, high-ranking NYPD sources said.

A neighbor who only gave her first name, Kristin, said she heard a man and Irigoyen arguing loudly and then the victim “yelling … about wanting to protect her baby.’’

Building super Lisa Raymos said surveillance video showed that “The first time, he stabbed her in the stomach.’’

Zereoue said he only saw the killer’s hoodie-covered head — and what looked to be a butter knife in his hands. Raymos said the suspect appeared to be in his 30s.

“I seen him dragging her down the stairs,” said Zereoue, who peered into the third-floor hallway after hearing Irigoyen’s anguished cries for help. “I seen her hands hanging on” to a hallway wall for dear life.

By the time Zereoue’s girlfriend called 911 and he ran down to the lobby of the 60-80 Myrtle Ave. building, Irigoyen was gasping for air, her loyal dog at her side, the neighbor said.

“She was at the bottom of the stairs bleeding out,” said Zereoue, 27. “She had a little dog with her, a pug, I think. Its feet were soaked in blood.”

The victim — a classically trained pianist who sold luxury homes and also worked as a professional Latin ballroom dancer and Zumba instructor — was stabbed several times in her neck and the left side of her stomach, police sources said.

She also had defensive wounds on both hands.

“She was fighting for her life,’’ a law enforcement source said.

The mortally wounded woman tried to name her killer but couldn’t choke out the words over the blood pooling in her throat, Zereoue said.

“I asked, ‘Do you know who he was?’ And she kept nodding yes and waving her arm,” he said. “She couldn’t speak.

“I kept telling her, ‘Hang on, hang on, help is coming.’ ”

Irigoyen was rushed to Wyckoff Hospital, but neither she nor her baby could be saved.

The killer was seen fleeing the building, and crimson bootprints revealed the first steps of his trail: east along Myrtle Avenue, toward Fresh Pond Road.

Detectives are poring over surveillance footage from both inside the building and outside neighboring stores for evidence, sources said. Police would not confirm its contents.

A police source said of the boyfriend’s possible involvement, “Don’t you think if your girlfriend got stabbed, you’d go to the police and say, ‘What happened?’? Well, he hasn’t come to us yet.

“He’s definitely a person of interest.’’

The stairs and black-and-white-tiled vestibule of the building remained stained red hours after the slaying. A pair of small black slip-on shoes were on the floor.

Raymos said Irigoyen was a quiet tenant who lived alone and kept to herself.

“She’s been here a year. She’s a sweetheart,” Raymos said.

The victim leaves behind a 12-year-old son from a previous relationship, sources said, adding that that child’s father is not suspected in Irigoyen’s death.

“She was a nice lady. She had a son. They were always together,” said Amar Mulamekic, the son of the super at Irigoyen’s former building in Rego Park. “I don’t know why someone would do this to her.”

Additional reporting by Shari Logan, Larry Celona, Sarah Trefethen and Tamar Lapin