A teen involved in a smash-and-grab robbery of a Michael Hill Jewellers store has been given a "crushing" sentence, with the judge saying this kind of offending has become "endemic" and a strong message of deterrence needs to be sent.

Cyress Martin has been sent to prison for six years for his role in an aggravated robbery of Bayfair's Michael Hill Jewellers, alongside a further aggravated robbery of a Whakatāne dairy.

Cyress was one of a group of six who donned masks, hoods and sunglasses, took up weapons and, after stealing two getaway vehicles, robbed the Michael Hill Jewellers store at Bayfair, Mount Maunganui, in January.

Cyress was armed with a knife while he and his co-offenders smashed cabinets, threatened staff and left with nearly $280,000 worth of jewellery.

Cyress was also involved in the robbery of Mananui Dairy in Whakatāne, where he'd kicked a victim in the head before stealing the cash register and tobacco products, using a stolen car as a getaway vehicle.

At his recent sentencing, Judge Thomas Ingram said the 18-year-old had a long and extensive criminal history and hadn't been helped by any of the rehabilitation efforts made by the courts to date.

Cyress had more than 20 convictions in the district court, along with a further 37 court appearances.

The judge says a point had been reached where "enough's enough".

"He has been before the court a great deal at 18, and to the extent the court has responsibility we've tried everything that can be tried and nothing has made the slightest difference."

He says Cyress shows no signs of rehabilitation and his offending kept going "on and on and on".

There was also a wider message that needed to be sent.

"Unless or until the courts approach offending of this kind with significant deterrent sentences then the offending is likely simply to continue as it has done over the last few years."

Cyress's lawyer Rachael Adams relentlessly advocated for him during sentencing.

She began by introducing Martin's social worker as the only person in attendance at his sentencing, other than lawyers.

"It says something, sir, that the only two people present for Mr Martin are two paid professionals, even by the appalling standards which we see regularly in this jurisdiction, this is a terribly sad story."

While she acknowledges the end result for Martin would be a term of imprisonment, and accepts the need for deterrence against aggravated robberies of this nature, she sought significant discounts for her client due to his age and background.

She pointed to his difficult start in life, which had almost certainly begun with the effects of fetal alcohol syndrome.

While she accepts he continued to reoffend, he had recently attended a restorative justice conference where he'd shown a "genuine flicker of acknowledgement that he's harmed someone else".

She submitted that with young offenders, it was important not to impose a sentence that was "crushing", and said the end sentence of six years, suggested by the judge, would seem "incomprehensible" to an 18-year-old.

"That's a third of his life," she says.

She asked for a discount of 20 per cent for his youth, as was applied to co-offender Cypris Buchanan. Buchanan was sentenced to two years, four months' imprisonment.

Judge Ingram says Cypris's record hadn't been as extensive and it had got to a point where Cyress's age and difficult background needed to be overtaken by the need for deterrence and safety of the public.

Rachael says she could not accept that at 18, it is too late for Cyress.

"I cannot concede that the point has been reached at which there is no prospect of rehabilitation."

Judge Ingram says there didn't have to be "no prospect", but it was best left to the Parole Board to determine when Cyress had been sufficiently rehabilitated and was ready for reintegration.

Crown Solicitor Anna Pollett says reports associated with Cyress's background and mental state made for difficult reading.

"But this offending is just not stopping and the protection of our community against such offending means a sentence of imprisonment is inevitable, and it's about the length of that sentence."

Anna says a pre-sentence report indicated Cyress has a high risk of reoffending and a high risk of harm to others.

Cyreaa had told a report writer he committed the robbery was because he'd had an argument with his girlfriend, felt angry and needed an outlet.

She acknowledges Cyress had spent 80 per cent of his adolescence in institutionalised care, but says the sentence must reflect the harm caused by the offending.

Anna says the offending had caused significant distress to the staff members present.

There had been threats to members of the public who'd tried to intervene, and the offending had taken place mid-afternoon when lots of people were around, perhaps including those who had just finished the school day.

She says the impact of this sort of crime, and the fear, was obvious.

Judge Ingram says the time for any sort of leniency was over.

"We've reached a point where you need a sentence which will deter you and perhaps others from this kind of behaviour."

The judge began with a starting point of six years for the Bayfair aggravated robbery and uplifted it by five years for the Mananui dairy robbery. By law, he couldn't uplift it further for a Whakatāne Michael Hill burglary that had taken place earlier because Cyress was 17 when that offending took place.

The judge made a further uplift of one year for the stolen cars used in the robberies, to reach an overall starting point of 12 years.

He didn't reduce it for totality, as was sought by defence counsel due to Cyress's age, however, the judge took Cyress's age into consideration in his decision not to uplift the sentence further for Cyress's prior offending.

The judge applied a discount of 25 per cent for guilty pleas, 5 per cent for "limited" remorse, 10 per cent for his age and 10 per cent for his background.

The judge sentenced him to six years' imprisonment, with no minimum non-parole period.

'Endemic' offending

Ram raids and smash-and-grabs of jewellery stores have hit the headlines repeatedly over the past few years.

Arthur Ashby, an 18-year-old who was part of group of armed thieves who stormed a Northland Michael Hill jewellery store and took more than $50,000 of products, was sentenced to three years and six months' imprisonment and will be required to go before the Parole Board for release.

Another 18-year-old, Te Peeti Melahkai Allen, was part of a group that targeted the Bayfair Michael Hill in March last year. He was sentenced to two years and 10 months in prison, which included uplifts for offending on bail and prior convictions, and discounts for his youth, guilty pleas and background.

Retail NZ's chief executive Carolyn Young says dealing with youth offending was complex, and retailers trusted the justice system to impose appropriate sentences based on the circumstances, background and offending.

"I think when we're talking about young people and their offending, it starts at the home and the support services we need to put around to ensure that young people have got the right support to make good decisions," she says.

But she says that they'd seen a significant rise in crime year-on-year for the last few years and it had reached an "untenable level".

She wasn't sure if troubled young offenders had the ability to process potential consequences ahead of committing offences, so would wait to see if tougher sentences brought a reduction in retail crime.

However, she says it would give retailers some assurance that the stress and loss associated with this kind of offending was recognised by the courts.

"They're looking for repercussions," says Carolyn.

"If someone gets six months for an aggravated robbery, where they've used weapons and terrorised staff and stolen expensive items, it doesn't seem that there's a balance. So after the fact, when something has occurred and someone's been arrested, the stores are looking for something equivalent to the action that's been taken."