Young Christchurch criminals using more violence during offences

A pair of robbers, including one disguised in a shark onesie, held up a petrol station in Canterbury. Photo / supplied via Police

The number of youth committing aggravated robberies in Christchurch is on the rise, with a criminologist saying it is only a matter of time before someone is seriously hurt or killed.

Police say there has been a small increase in the number of youth committing crime, but the bigger concern was the severity of the crimes being committed like aggravated robbery.

"Weapons are being used by youth during robberies. Sometimes even firearms during robberies, which is a huge concern to us, as the risk of someone getting hurt is very high," Senior Sergeant Phil Newton said.

Police data shows, in 2015, there were 22 aggravated robberies committed by offenders between the ages of 10-19, with 29 in 2016 and four in January.

Canterbury University criminologist Greg Newbold said it was only a matter of time before shopkeepers took matters into their own hands, including the use of weapons.

Canterbury metro commander Superintendent Lane Todd strongly advised retailers not to take the law into their own hands.

"The risk [of injury] gets heightened quite quickly when people fight back and that is the last thing we want," he said.

He said police advise anyone confronted by an armed offender to fully comply and then phone 111.

"While we have had a recent spike in armed robberies we have had quite a high success rate of apprehending these offenders and dealing with them through the courts," he said.

Senior Sergeant Newton said there is often little reward for the robbers.

He said the maximum penalty for aggravated robbery is 14 years in prison and police were "amazed at the huge risks taken for so little reward".

"It is very rare that offenders get away with more than $1000; it is more like a couple of hundred," he said.

In October last year, two 13-year-old boys and one 15-year-old girl were charged with the aggravated robbery of the Challenge Opawa Service Station.

The trio of robbers, all wearing masks and brandishing weapons, took more than $5000 worth of tobacco products along with $300 cash and were arrested a short time after, at a nearby address.

On Tuesday, two youth appeared in court for allegedly robbing BP Rolleston with a knife and hammer. One of the offenders wore a shark onesie and they made away with a pack of lollies.

Newbold said a combination of cultural influences and lack of parental control is allowing youths to do "whatever the hell they like".

"There is a direct influence of the gangs in America and the black rap culture on the youth in this country," he said.

He said the drive behind the escalation of the crimes they are committing could be one of two reasons -- addiction or bravado.

Police are working with business owners who have been victims of robberies in an attempt to make them "harder targets".