A 19-year-old man has had his prison sentence reduced on appeal for a five-hour night-time crime spree which earned him seven convictions, including aggravated robbery, kidnapping and indecent assault.

Tyreece Kohe-Davis was sentenced to four years and three months in prison when he appeared before Judge Thomas Ingram in the Tauranga District Court in February.

He had pleaded guilty to aggravated burglary, indecent assault, demanding with intent to steal, aggravated robbery, kidnapping, injuring with intent to injure and possession of an offensive weapon.

The charges related to three incidents involving three victims in the Bay of Plenty area through the night of February 4 and 5 last year.

Kohe-Davis appealed his sentence to the High Court, arguing that it was "manifestly excessive" because the sentencing judge failed to give him enough of a discount for his youth and other factors.

High Court Justice Graham Lang allowed the appeal, cutting 10 months off his total sentence, to three years and five months.

Kohe-Davis' night of crime began when he kicked open the front door of a house near Te Teko about 10.30pm on February 4, while carrying a knife.

The High Court judgment said a pregnant woman was alone in the house at the time and Kohe-Davis was accompanied by two other men, one wearing Mongrel Mob regalia.

Kohe-Davis, who was looking for the woman's partner, left after telling the woman she was pretty, grabbing her breasts and buttocks, and kissing her on the cheek.

About an hour later, Kohe-Davis threatened a man at a service station with a knife, demanding money and telling him to hand over his vehicle.

The man refused both demands, telling Kohe-Davis he would need more than a knife if he wanted to take the car.

Kohe-Davis and his associates then drove away but about two hours after that, they attacked a man who had stopped his car on a road near Kawerau to urinate behind some trees.

Kohe-Davis punched the man in the face, and with his two associates, hit and punched him over an "extended period", continuing when he was on the ground, the judgment said. Kohe-Davis also held a knife to the man's throat.

Kohe-Davis then opened the car boot and told the victim to get inside, which he did.

Kohe-Davis and the other men left after failing to start the victim's car, which had a flat battery.

When they left, the victim found that his cellphone, wallet and medication had been stolen.

When Kohe-Davis received a sentence indication in August last year, the judge indicated he would "probably" get a 25 per cent discount for his youth, and he then pleaded guilty.

When he was sentenced, however, only a 15 per cent discount was given for youth, contributing to a total discount of 50 per cent once the guilty plea and other factors were taken into consideration.

Kohe-Davis argued that more of a discount should have been given for his youth and other factors identified in a cultural report.

That report said that Kohe-Davis had been brought up in a gang environment, marked by drugs, alcohol and violence.

Justice Lang said there was likely to have been a "nexus" between the negative aspects of Kohe-Davis' upbringing and his offending, and gave him a total 60 per cent discount from the sentence starting point of eight years and six months in prison.

- Ric Stevens, Open Justice