WARNING: This story contains descriptions of child abuse and may be distressing to some readers.

A judge has urged people who work with children to speak up if they suspect abuse is happening, after 5-year-old Malachi Subecz was murdered by his carer.

Malachi died from injuries inflicted by Michaela Barriball in Te Puna in November last year, after months of violent beatings and neglect. He had been placed in Barriball's care at the request of his mother, who was in prison.

On Thursday, Barriball was sentenced to life imprisonment for her offending and will spend a minimum of 17 years in prison before she becomes eligible for parole. The sentence is one of the longest for a female offender in New Zealand history.

High Court Justice Paul Davison spent more than an hour in the sentencing hearing in Rotorua detailing the abuse Malachi suffered, also offering his own view on the important lessons that must be learned from the case.

"The tragedy of Malachi's death provides some strong and clear lessons to everyone involved in the care of children," Davison said.

Michaela Barriball was sentenced to life imprisonment with a minimum non-parole period of 17 years - one of the longest ever sentences for a female offender. Photo / Andrew Warner

"In the circumstances of this case, it appears there were a number of adults who observed Malachi showing signs of suffering injuries, which they suspected might have been deliberately inflicted."

Those observations were detailed in the summary of facts.

In one example, Malachi was dropped off at his Tauranga daycare in September. His hairstyle had been changed, with his fringe pulled over his forehead.

Under the fringe was large swelling. He also had a black eye, bruises, and a scratch under his chin.

Barriball was spoken to by staff at the daycare, where she explained Malachi had fallen twice off his bike.

The daycare staff later asked Malachi if that was the case. He said no. As staff attended to his injuries, he told them Barriball "would be mad" at him.

There were also a number of text messages referring to the abuse sent by Barriball to her partner.

"Malachi was also suffering the effects of malnutrition," the judge explained. "It would have been apparent to those close to him."

Malachi weighed just 16kg at the time of his death - the same weight recorded by a doctor two years prior when he was 3.

"Unless responsible adults are prepared to speak out and contact the police, the opportunities to prevent further trauma or damage to the child are lost," Justice Davison said.

High Court Justice Paul Davison, pictured here in 2012, said it is a "community responsibility" to alert authorities to suspected abuse. Photo / NZME

"This is a community responsibility, and leaving it to others to act can so easily lead to tragic consequences such is the case here."

Oranga Tamariki is investigating its involvement during Malachi's short life.

In May, Oranga Tamariki chief executive Chappie Te Kani said the investigation was an "absolute priority" for the government department.

"We need to get to the bottom of why this happened, whether there was more we could have done, and what we can do to ensure such an awful tragedy never happens again."

Outside court in the moments after Barriball's sentencing, Malachi's aunt Helen Menzies said the whānau was hoping the outcome of the investigation would lead to closure.

She was among a group of whānau dressed in clothing printed with #Justice4Malachi.

"It is our hope as a family that the significant failings become apparent in this investigation and that all failings within the system are fully addressed with legislative changes to follow.

"When this happens, we know Malachi's voice will have been heard."

- Ethan Griffiths, Open Justice

If you have concerns about the immediate safety of a child, call 111. Alternatively, call the police non-emergency reporting line on 105. Or, contact Oranga Tamariki, Ministry for Children on 0508 326 459 for advice or click here to visit the agency's website for more information.