The Department of Internal Affairs says five people in the past two months have been jailed for trading in images of child sexual abuse.
Benjamin Masters, 31, of Lyttelton, was sentenced on Friday to a prison term of 22 months.
Internal Affairs says he was caught during an online chat with an undercover Australian policeman.
During the chat session, the policeman was sent a video clip and more than 40 images depicting the sexual abuse of children, including babies and toddlers.
No evidence of sexual offending was found.