Almost 200 young offenders were held in police cells last year for periods of more than 24 hours and, in some cases, up to seven days.
In one case a young offender in Nelson spent six nights in a police cell before a judge ruled it was untenable to hold him there any longer.
The boy's lawyer, John Sandston, said that since then, none of his young clients has been held in a police custody for more than 24 hours.
He said while community remand homes were the better choice for holding young offenders, it could be a struggle to set them up.
"Not many people would want to have young offenders living over their back fence particularly if they've got children of their own," he said.
"The kids are often ... they're on quite serious dishonesty charges like aggravated robbery so it is going to take time unless you set up these remand places quite some distance from households."
In July, 17-year-olds will be brought into the youth justice system, meaning it will need to cater for up to 1600 more young people a year.
Mr Sandston said he worried that would put more pressure on an already stretched system.
The Children's Commissioner, Judge Andrew Becroft, said young people should not be detained in police cells, and has repeatedly called for the practice to be banned.
He said while it was encouraging that the number of young offenders being held in cells was down 30 percent from the last year, the figures had always fluctuated.
But he was optimistic there would be enough facilities available so the numbers of youth offenders in cells would not explode in July.
"Theoretically there is always that risk but we've known about the law change for sometime now, there's good preparation being carried out, there will be a suite of options available - custody's not the only option."
Judge Becroft said the only time it might be warranted to hold a young offender in a cell was before their first appearance in the Youth Court.
Phil Dinham from Oranga Tamariki said a cell was sometimes the only option.
It could be difficult to move the young offender out of the cells to other accommodation if they posed a safety risk to themselves or the public, he said.
"What happens then is us and the police will provide a duty of care to those young people and make sure that they're fed, their safe, they have any medical attention they need.
"While it's not ideal and while we're moving in the right direction, it'll be a while yet before we can completely eliminate that."
Mr Dinham said he accepted that a police cell was not the right place for a vulnerable young person, but holding them there wasn't against the law.
He said the number of young offenders spending more than 24 hours in a police cell was not expected to noticeably increase come July.
Mr Dinham said that was because youth crime was down, and agencies were working hard to deal with low level offending through pathways outside court like police diversion.