Walker said the teenage girl was arrested at 4.20am and charged in relation to an assault and robbery in Wellington's CBD earlier in the night.
A number of other youths were also taken into custody at the same time.
"At 6.45am several of those youths were transported by police to their home addresses," Walker said.
"The girl was not transported along with those youths, but was meant to be waiting for her mother to collect her from the station. "
Walker said sometime between 7am and 8.30am police staff involved in the arrest of the teen phoned her mum and asked her to pick her up, then placed the girl in an interview room until she arrived.
"At around 3pm police received a call from the girl's mother, asking if we knew her whereabouts.
"The girl was still in the interview room, where she had fallen asleep. When police confirmed the girl was still in an interview room, she was immediately taken home," Walker said.
Police Association president Chris Cahill told the Herald "it simply isn't good enough" for a 14-year-old girl to be kept in a locked room for a lengthy period of time.
However, Cahill said the situation highlighted a difficult scenario for police staff if they were unable to contact a young person's parents.
"We really have no other facility to take them to. More often than not, in many cases, it is nowhere near appropriate to put them in police cells.
"It wouldn't be a good environment for a young person."
He said the lack of resources to properly process and hold a young person "creates some real issues".
"Essentially we become babysitters to a certain degree."
While reiterating it "wasn't good enough" to hold the teen in a locked room, he said arrested youths can, at times, be left waiting for their parents.
"Often we have parents that take an exorbitant amount of time to come and collect their children," he said.
Police explained the circumstances of the girl's arrest and time in custody personally to her mother and also reported the incident to the IPCA.
Since the girl was kept in the interview room, Wellington Police have made changes to shift changeover processes to prevent a recurrence of such an incident.
