But the Ngaruawahia baby's life was cut s' />

Six-month-old Serenity-Jay Scott-Dinnington had just learned to crawl and was her mother's "lil angel".

But the Ngaruawahia baby's life was cut short yesterday when she died in the Starship hospital from injuries police say were not accidental.

Her life support was switched off in the afternoon, and she died at 4.35pm surrounded by family members.

Police have upgraded their investigation to a homicide inquiry, and said a post-mortem examination would be conducted this morning to determine how Serenity died.

The little girl was taken to hospital on Tuesday after an "incident" at the Havelock Rd house where she lived with her mother, Chelsea Scott, 21.

While Miss Scott went with her daughter in the ambulance, her brother Drew Scott - who also lived at the house - and her fiance, Mathew Ellery, were taken to the Huntly police station for questioning.

It is understood Mr Ellery went to check on Serenity and yelled to Miss Scott for help.

Mr Scott also ran into the baby's room and after seeing her, believed she was dead.

Mr Scott could not be reached last night, but earlier told one media outlet that he was watching TV when he heard his sister scream "help, help".

The rest of the ordeal was a blur as Chelsea and Serenity left for the hospital, he said.

On her Facebook page, Ms Scott described her daughter as "so cute".

"Our lil angel," she wrote. "Im so proud of my little gurl! I was just told by a Plunket lady that Serenity is the youngest baby she knoz of 2 b crawlin around ... Shez a clever little gurl!"

Miss Scott's mother Celeste Scott sobbed yesterday when she heard that her granddaughter had died.

"I'm totally freaking out ... Oh my God, I can't believe she didn't make it to eight months old," she said. "I don't know what to think, to be honest."

Mrs Scott had not been able to reach her daughter.

She said it was shocking to think one of her family could be responsible for Serenity's death.

"Oh my God, it could be anyone. It's disgusting. I just want to know what the hell happened."

Mrs Scott said Serenity was a cute, quiet and "very mellow" baby.

"Chelsea was a good mum. She's always been a great mum to [her other child] Travis and Serenity."

Police would not be drawn on the nature of Serenity's injuries.

"Obviously this is a sad development in this case," said Detective Senior Sergeant Mark Greene.

"Our focus is very much on determining the events leading up to the baby's admission to hospital and her subsequent death."

CYF said on Wednesday that Serenity and her family were "known" to it but refused to give details of its involvement.

Serenity's 4-year-old brother Travis was now in CYF care.

"The injuries suffered by this baby girl are tragic and our thoughts are with her and those who love her," said CYF head of operations Jo Ann Field.

Jessica Dinnington, whose brother Zane was in a relationship with Miss Scott for about a year before she met Mr Ellery, told the Herald she was saddened by the events.

She said Serenity took her family name as well as Miss Scott's surname but a DNA test showed her brother was not her father.

"She's not Zane's, but he was the partner to her when she moved into Ngaruawahia," she said. "He stayed with her right through her pregnancy."

Figures released under the Official Information Act show 130 children were admitted to the Starship with injuries from "definite or probable" child abuse between July 2005 and July last year.

Including Serenity, 18 children have died in the Starship from such injuries.

Other high-profile cases include twins Chris and Cru Kahui and Nia Glassie.

The chief executive of advocacy group Child Matters, Anthea Simcock, said Serenity was the third child she knew of to die in similar circumstances this year.

"And that's three that didn't need to die."