A 9-year-old girl hanged herself in her Bronx home — after her mother told her it was too early in the morning to be on her cellphone, sources and neighbors said Sunday.

Heaven Vega was found dead by her horrified mom, Jennifer, in her bedroom at the family’s apartment in the Bronx River Houses shortly before noon Saturday, authorities said.

The child had tied a belt around her neck and hanged herself from her bed, police said.

Earlier in the morning, the mother and daughter had fought over the girl’s cellphone use, police sources and neighbors said.

“Nowadays, all kids have cellphones in their hands, and all they do is watch YouTube,” said a neighbor who didn’t want to be named. “Apparently the girl woke up, and she wanted to get the phone to go on YouTube. But the mother told her, no, it was too early in the morning.”

Next-door neighbor Zoraida Irizarry said the child’s grief-stricken mother is now blaming herself for the tragedy.

“I can’t imagine what the mother is going through right now. A friend of mine spoke to Jennifer, and Jennifer said that she thought that it was her fault,’’ she said.

The distraught mom called 911 after finding her daughter in the room, a source said. One of Heaven’s brothers performed CPR until paramedics arrived, the source said.

“I can hear into their apartment through my wall,” said Irizarry, who lives next door to the family’s third-floor apartment.

“Yesterday morning, I heard the older daughter calling for her sister at a regular tone, and then all of a sudden her voice got really loud, and she started screaming.”

The little girl was rushed to St. Barnabas Hospital but could not be saved. It’s unclear whether she left behind a note.

Neighbors in the building said Heaven was the youngest of four siblings, and recalled that all of the kids would sit in the hallway glued to their phones.

“I don’t get it. She always had a smile on her face. I only ever saw her happy,” Irizarry, 59, said of Heaven. “I would come home and she would be sitting in the hallway doing her homework, I guess because it was quieter out there.”

She said the entire community is in shock over the girl’s death.

“I don’t know how her mother can function after this,” she added.

The grieving mom could not be reached for comment.

Additional reporting by Stephanie Pagones