A young woman was hacked to death and another was seriously hurt by an ax-swinging maniac who turned a Brooklyn apartment into a scene out of an 80s slasher flick — carnage that unfolded early Saturday within earshot of a 4-year-old girl who was in a back bedroom, sources told The Post.

Police on Saturday afternoon were looking to question the surviving woman’s ex, but had not yet located him, sources said.

The savagery came to light at 1:30 a.m., when blood-drenched mom Angela Valle, 21, called an Uber to 811 Flushing Avenue in the Bushwick Houses, police sources told The Post.

Valle had suffered a life-threatening blade chop to the back of her head, along with gashes to her chest, arms, stomach and throat, sources said — and although she asked to be driven to the hospital, the Uber driver immediately called 911.

The gravely injured woman was able to tell medics two things before losing consciousness, sources said.

One was that her ex-boyfriend had attacked her and her friend, whose dead body was still inside the eighth floor apartment, sources told The Post.

The other was that her little girl, Aliana, was also inside.

Police rushed to the apartment, and found a horrific scene.

A woman was lying on the living room floor. She had been partially decapitated. Some of her fingers had been severed. There were more stab wounds throughout her head and body.

Police identified the slain woman as Savannah Rivera, 20, who lived at the address. She was pronounced dead at the scene.

Valle’s daughter was found sleeping and unharmed in a back bedroom, sources said. She was taken to Woodhull Medical Center for evaluation, police said.

Investigators later found what they believe to be the murder weapon — an ax, still smeared with blood, that had been tossed into a trash compactor in the building, sources said.

Valle, meanwhile, was at Elmhurst Hospital Center in critical but stable condition with “severe head trauma,” police and sources said.

“My daughter, Angela Valle, was injured,” her mother, Jessica Cruz, told The Post via text from the hospital. “I have no more information as the cops aren’t telling me much right now.

“Right now, my family and I are trying to cope with what’s going on,” she added, calling her daughter, “my main priority.”

Little Aliana was adorable and well-cared for by Valle, said neighbor Renee Hamilton, who lives on the 16th floor.

“I ride the elevator with her in the morning and she’ll be taking her little daughter to school with her every morning,” Hamilton said.

“Me and my daughter ride the elevator with her. I always comment on how cute the little girl looks in the uniform.

“I never seen her with a guy. I feel so sorry for her. I’m gonna pray for her. It’s crazy. We got police in the building. That’s like shocking to me.”

Additional reporting by Tina Moore, Adam Schrader, Stephanie Pagones, and Laura Italiano