Warning: Contains confronting information from court

A man who had just brutally beaten - and killed his partner - sat with their beaten baby outside their rural Matamata home for hours after the attack.

Paraki Edwards' "frenzied" attack was so vicious that it has left the toddler diagnosed with cerebral palsy due to the extensive and serious brain injuries he suffered on the morning of Christmas Eve 2018.

Edwards, 42, had earlier admitted the murder of Michelle Kayla Hurinui and causing grievous bodily harm with reckless disregard to their then 1-year-old toddler.

Edwards was due to stand trial in July last year but he changed his plea during an appearance in May. He was jailed for 16 years on all charges.

Hurinui, who was a mother of six children at the time of her death, had her relatives, including her parents and siblings in the public gallery to hear Edwards be sentenced by Justice Graham Lang this morning.

In pushing for a 17 year starting sentence, Crown prosecutor Rebecca Mann told the judge that the fact Edwards remained at the house, hiding a phone, lighting a fire, and not seeking medical assistance for their 1-year-old baby who was seriously injured in the attack which Edwards admitted was "frenzied", spoke of the callousness of what happened.

Hurinui's bloodied body was discovered by her older brother after he returned home from work.

She had so many injuries and been struck by a "sharp object" so many times that they had been unable to determine exactly how many blows she had suffered.

Mann said they instead could only say that it was "substantial".

Edwards had told police that the attack had lasted "no longer than" eight minutes.

Mann said if that was true that was still a long time.

The court heard the pair had an argument on Christmas Eve about where their toddler would spend Christmas Day.

Edwards used not only his fists to beat Hurinui but also a child's bubble toy and the impact of smashing it against her was so horrific the toy disintegrated; a post mortem report found pieces of plastic embedded in her skin.

Pieces of shattered glass were also found from the use of a picture frame and glass from a ranch slider door.

Aggravating the offending was the fact Hurinui was holding their baby at the time and also suffered significant body and brain injuries.

After the attack, Edwards covered her with a blanket and called various members of his family.

However, he never sought medical assistance and emergency services only arrived after being contacted by Hurinui's brother who arrived home from work.

In the several hours he remained at the house afterwards, he changed his clothes, cleaned himself of Hurinui's blood, hid a cellphone under the house and burnt another one in the fireplace along with the remnants of the picture frame, used in the attack.

He put the seriously hurt toddler in a baby capsule and sat outside barefoot.

When her brother asked what happened, Edwards said "it's not good".

"I have killed her. Your sister bashed my son so I had to stop her."

Emergency services arrived to find the toddler ashen in colour and with a swollen left eye and face. He was airlifted to hospital and further injuries were discovered including a skull fracture, fractured forearm and extensive bruising on his body.

The toddler has since, and continues, to suffer from seizures and the diagnosis of cerebral palsy due to the brain injury.

Edwards' lawyer Paul Borich QC submitted that his client heard a "slapping" noise before turning around seeing Hurinui hit the baby.

It was then that he hit Hurinui, and "completely lost it".

"When he finally gained control he realised what he'd done. He stayed at the scene and has to accept that he didn't seek medical attention. but when family arrived and police arrived he still stayed there."

However, Edwards staying at the scene and not fleeing and the fact that he struck Hurinui after claiming she had hit the baby, was a mitigating factor, Borich said.

Edwards didn't have an explanation for not seeking medical assistance, "he could have done better and could have sought medical attention ... and confessed to doing what he physically did".

Borich said there was "no answer" as to why he didn't seek medical assistance and added that Edwards had contemplated suicide after killing Hurinui but it was "concern for his son that was the reason that he didn't do it".

Borich sought a base sentence of 11-12 years before asking the judge to add uplifts for offending against the toddler.

Edwards had claimed that he performed CPR on Edwards, however, that was dismissed by Justice Lang as a lie.

Justice Lang acknowledged the victim's family in court as he began his sentencing and admitted there was nothing the court could do to bring her back or repair the damage done to their child.

Hurinui's mother, Sharon, told the court she, her partner and Michelle's child had to uproot their lives from Australia and move back to New Zealand to care for the toddler who was injured, and continues to deal with injuries that were suffered.

She said the loss of her daughter had fallen heavily on her shoulders as she'd had to stay strong for the rest of the whānau.

Edwards himself also read a letter of apology to the court - not before three members of his family left the court room - and Hurinui's family, expressing his remorse and understanding of the hatred they would feel towards him about what he did.