A teenager involved in a smash-and-grab of a jewellery store has been sent to prison for six years

Open Justice reports Cyress Martin was one of six who donned masks, hoods and sunglasses, and -- after stealing getaway vehicles -- robbed a Mount Maunganui Michael Hill Jewellers.

The 18-year-old was armed with a knife, while the group smashed cabinets, threatened staff and left with jewellery worth nearly 280-thousand dollars.

Judge Thomas Ingram says Martin has a long history of crime and hasn't been helped by rehabilitation efforts.

He says this type of offending has become endemic, and a strong message of deterrence was needed.