The Human Rights Commission says a review of the practice of holding young people in police cells is vital to stop it continuing.
The review is being carried out to meet obligations under a part of the United Nations Convention Against Torture which New Zealand joined in 2007.
The project will be run by the Independent Police Conduct Authority, the Children's Commissioner and the Human Rights Commission.
Chief human rights commissioner Rosslyn Noonan says young people should not be held in police custody for more than 24 hours.
Ms Noonan says the practice was almost stopped five years ago and must not be reversed.
Youth advocates say the review has to find ways to stop the practice altogether.
After almost 700 young people in 2006 spent time on remand in police cells, the practice was almost done away with, but there is evidence it is creeping back in.
Criminal lawyer Jim Boyack says putting young people into police cells for up to a week is tantamount to torture and the review must find ways to eliminate it.
Mr Boyack says the problem reoccurs whenever there is a shortage of beds in secure residences.
A senior solicitor at Youth Law, John Hancock, says the review should look at the Government's tougher sentencing laws which are putting pressure on secure beds for young people.
Mr Hancock says he keeps hearing that young people are being kept in cells for multiple nights again, even though it is meant to be an absolutely last resort option.