Police have come under fire for failing to investigate a case of suspected child abuse or give priority to an emergency call.
The police watchdog has released a report over the incident in 2013, when central Auckland police responded to two incidents at a Mt Wellington home.
In September, police received an emergency call that a woman and her son were being held against their will by gang members and the boy had been punched in the face.
However the emergency call was not followed up immediately, as no police cars were available.
After visiting the family in hospital, police became suspicious the boy's injuries were caused by child abuse, but did not notify a child protection team.
Officers failed to record the complaint and include documents before sending the case to Counties Manukau.
The Independent Police Conduct Authority found it was their responsibility to initiate follow-up enquiries, and by not doing so, they failed to fulfil their duty.
Authority chair Sir David Carruthers said it was crucial all police officers were open-minded to the various possibilities when dealing with a child who had been injured in unusual circumstances.
"The immediate and ongoing safety of a child must always be the first priority.
"Consequently, it was unacceptable to presume that another officer would raise the flag."
It acknowledged the situation was complicated by the fact the incident and response took place across two different police districts.
However, all officers working in the wider Auckland area should have a good understanding of police protocols for dealing with cases across districts, he said.
Police have accepted the authority's findings and say they have provided further training to Auckland frontline staff to ensure they follow correct processes.