Youth gang members are bragging on social media about committing robberies and other crimes.

Youth gangs across New Zealand are taking to social media to brag about violent crimes, including robberies and ram raids.

Some post security footage of robberies, news articles about the crimes, and photos of them with the supposed loot on their Facebook pages and on YouTube.

The gangs recruit members, aged 15 and up, while serving time in youth justice facilities or prison.

One of the gangs, We Strait Aych (WSH), is understood to be responsible for a series of robberies at a Christchurch Night 'n Day store over six months.

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The Ferry Rd store's staff were threatened with pistols, machetes and knives by masked youths targeting cigarettes and cash. Fifteen people were arrested.

In March last year, one We Strait Aych member posted a photo – featuring the words "straight outta YJ (youth justice) South" – on Facebook of him allegedly robbing the Night 'n Day. In a video uploaded to Youtube in May last year, group members posed with hundreds of dollars cash spread across a bedside cabinet.

Another video by a gang called Teamoneyaffendersz, posted in March last year, included media coverage of a Stirling Sports store in Waikato being ram raided. It was followed by a video showing sports goods in the back of a car.

SUPPLIED Footage posted on Youtube by youth gangs appears to show stolen cigarettes and cash.

Night 'n Day chief executive Tony Allison said it was beyond belief that the offenders allegedly responsible for robbing his store with hammers, machetes and pistols were boasting about the incidents online.

"To sensationalise something like that, a traumatic event for a staff member it's just unbelievable."

Allison said there was something wrong with the system if the youths could bolster their numbers while serving time for offending.

Canterbury police area prevention manager acting Inspector Paul Reeves was appalled by the online boasting.

"The footage is disgraceful and we've got to look at the people who are actually working in these dairies, they've got families they want to go home to safely and they shouldn't be subjected to any of this behaviour. For people to actually go online and brag about it is disgraceful."

He said police focused on working with youth to ensure they were not offending and to prevent further risk to the community.

One young gang member claimed the offending was motivated by boredom, which Reeves said police were happy to help with.

"If they do want to enrol in courses or if they want assistance to find something to do then approach police. We can find them a course to go on and work with organisation that can keep them motivated and occupied."

SUPPLIED A group of youths pose after allegedly breaking into a sports store in Waikato.

Allison said while the robberies had stopped in Christchurch, he was still having issues in Auckland. Last weekend, a group reversed a car into a store several times to try to steal an ATM.

Stuff approached several members of WSH on Facebook. Most did not respond to requests for comment.

One member based in Wellington, who cannot be named because of his age, said the gang started as a small group of teenagers in Auckland in 2015. Factions had since emerged in other parts of the North Island and in Christchurch.

He said the gang was split into three groups: WSH, Hu F….. Kares (HFK), and Grey Kolor Offenders (GKO). The groups all wore grey, but were "different cliques".

"Basically it's a competition to prove who is the best out of whoever reps the grey colours ... to show who is better in crime and who is more higher up."

The youth, who claimed he had spent time in Palmerston North youth justice facility Te Au Rere a te Tonga and three months in Rimutaka Prison for aggravated robbery, said there were several ways people joined the gang, with most members recruited while inside a youth justice facility or prison.

"As soon as someone goes to jail they get jumped into the gang in jail ... and some come out of jail and then get into the gang."

GEORGE HEARD/STUFF The Woolston Night 'n Day on Ferry Rd was robbed nine times in six months.

Asked why the gangs committed crimes, he said it was "just a youth thing".

"We've got nothing to do, it's boredom. We've got no money. We're just trying to grow up and it's not easy in life and just trying to make something.

"Some of the guys in the gang are fearless, but some of us are not out to harm anybody, we're just trying to make money for ourselves. People think we're out to harm people like the Black Power or Mongrel Mob, but we're more against the law; we just don't like the law."

Oranga Tamariki youth justice residences general manager Ben Hannifin declined to comment on WSH recruiting members while in youth justice facilities, citing security and privacy concerns.

He said residences had a high turnover, with young people coming and going every day.

"Gangs or similar anti-social behaviour is often quite transient and depends on relationships built and friendships or connections made between young people which continue on when they leave residence."

A transition to a supportive community delivered the best outcomes for young people and was more likely to help end to their association with anti-social peers, Hannifin said.

"It is always a concern and unfortunately not a new phenomenon, but it is an area we are always working to improve on."

SUPPLIED Police say the footage is "disgraceful".