Liam Burrowes, 16, has been jailed for three years for two armed robberies of the Woolston Night n' Day store on Ferry Rd, Christchurch.

A teenager will serve an adult jail sentence for two armed raids on a Christchurch dairy that left his victim fearing for his safety and struggling to sleep.

In the Christchurch District Court on Friday, Judge Stephen O'Driscoll told Liam Burrowes: "Aggravated robberies are not games. The stakes are high."

He jailed the 16-year-old for three years for the Woolston Night n' Day robberies. The teenager will be in Christchurch Men's Prison's youth wing.

The judge warned that future youth offenders might not be spared prison terms on their age alone.

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"I hope the sentence I have imposed will not just deter you, but will deter others in the community who may be contemplating this perceived game," he told Burrowes.

Aggravated robberies – robberies involving weapons or multiple offenders – carried a maximum 14-year jail term and had the potential for serious consequences for vulnerable shopkeepers, Judge O'Driscoll said.

Tony Allison, who owns the Ferry Rd store, said he was happy the teenager had been jailed.

"It does send a signal to say you can't just do this stuff [as a youth] and expect no consequences. It is a pretty serious crime and a lot could go wrong," he said.

"I guess my view would be hopefully in that time [Burrowes] can come to a sensible decision about how to lead his life."

Allison said new security measures had prevented the most recent robber – the dairy has been robbed 10 times in eight months – from escaping with much. A masked daytime intruder fled the store when he could not access the till or cigarettes on April 18.

"One, they're getting nothing; two, they're getting caught apart from the very first one; and then three, if you're going to get a sentence of three years at that age, or more if you're older, you'd absolutely say it's not worth it at all."

Staff were doing well "under the circumstances", he said.

"And we're providing as much assistance as we can and trying to keep an eye on things."

When Burrowes was interviewed for his pre-sentence report, he told the probation officer he was surprised to find himself being sent to the district court for sentencing. He had thought that if he was caught he would get the maximum youth justice sentence – supervision with residence, which was effectively youth prison.

The judge decided the offending was serious enough for an adult sentence, particularly considering his record and his recent release from a Youth Court sentence when the first robbery took place on December 3.

In that robbery, a disguised Burrowes and two co-offenders with hammers entered the store at 4am. Burrowes carried a sports bag for the loot and a small axe. Cash, cigarettes and tobacco products worth $1565 were taken and the shop assistant was threatened with a weapon.

Burrowes went back on December 22 at 4.50am, again armed with an axe and wearing gloves, a bandanna and a hooded sweatshirt. Cash and tobacco products were again targeted.

The same shop assistant was robbed both times. He had now been robbed four times.

The shop worker said he was having trouble sleeping and did not feel safe. He had not worked a night shift since Burrowes' last robbery.

"He has not told his family about what has occurred because he is concerned his family may want him to leave New Zealand and go back to India," Judge O'Driscoll said.

He said he was not sure why that store was targeted so much. It may have been seen as a "soft" target, where the shopkeepers did not resist, or simply an easy way of getting cash and cigarettes.

The judge reviewed other cases where young people had been sentenced for dairy robberies, including some at the Woolston store. The sentences had ranged from Youth Court sentences of supervision with residence to supervision with activity, and one term of two years, seven months' jail.

Judge O'Driscoll said Burrowes was young, but his offending had not involved typical youth behaviour. There had been multiple offenders, disguises, weapons and premeditation, as well as two robberies.

He said offenders who committed aggravated robberies could not expect their youth would mean they would get supervision with residence sentences.

The automatic name suppression applied in Youth Court was lifted once Burrowes was transferred to the district court.

Children's Commissioner Andrew Becroft said he was unable to comment on the judicial process.