The Principal Youth Court Judge says police cells have become more than a short-term last resort for young people.
A review by several agencies has found 213 children under 17 were held in police cells for more than 24 hours last year compared to 76 in 2009.
The review, by the Independent Police Conduct Authority, the Children's Commissioner and the Human Rights Commission, has made 24 recommendations including introducing better training and reporting.
Judge Andrew Becroft says the reason for the rise is perplexing, as the numbers dropped significantly in the middle of last decade, and the latest figures are a reminder that the system must do better.
"We need to remember that young people in police cells are vulnerable, they're developmentally at a very pivotal stage," he told Radio New Zealand's Morning Report programme.
The judge says no-one can predict what solitary confinement is going to do a young mind, and lives can be put at risk.
Lawyer warns of dangers
Hastings youth lawyer Don Kennedy warns that it is only a matter of time before the increasing trend of holding teenagers in police custody leads to a tragedy.
Mr Kennedy says the youth suicide rates in this country are atrocious, and while the police take every precaution, and do things like put young people on watch, the young people can be fairly inventive.
He told Nine to Noon that ensuring young people are kept safe will require more resources.
The Law Society youth justice spokesperson, Michael Gardam, says the organisation is looking forward to developing the review's recommendations, though he is not confident the money is there to support all of them.
Mr Gardam says some suggestions, such as improving information-sharing, will be able to be implemented cheaply and quickly, but finding additional places for teenagers could prove costly.
Director of the lobby group Rethinking Crime and Punishment, Kim Workman, says there seems to be an attitude that holding young people in rough conditions will teach them a lesson, whereas evidence shows it has the opposite effect.