A Northland man who spent 15 years sexually and physically tormenting his step children, has sentenced to given 20 years in prison - with no discounts

Open Justice reports the 56-year-old was found guilty of 48 sexual and violent abuse of children charges in December last year.

During impact statements, the three now-adult victims say the man stopped them from having friends and going to school, so he could abuse them.

Judge Peter Davey says the man continues to deny responsibility, and his character referees were ignorant of his actions.

He can apply for parole after nine years.