The unexplained death of an infant in Dargaville earlier this year is being investigated by police.
The sudden death of 10-month-old Kween Thompson was reported to police in July 2023, Detective Senior Sergeant Kevan Verry said.
But Verry said police were not notified of potential unexplained circumstances until the days following the death.
"It was in these following days police were made aware of a non-accidental injury, which is now the focus of a child protection investigation.
"As part of that investigation we are looking into the circumstances of the death, which at this stage is being treated as unexplained."
Verry said that it appeared the non-accidental injury did not relate to the death.
"However, we can confirm the cause of death has been determined to be asphyxia," he said.
"Police, including Dargaville CIB and the District Child Protection Team, are making enquiries into this matter, and are gathering facts about events on the day of baby Kween's death from a variety of sources."
Verry said police were working with medical experts to understand more about the injury, which could take some time.
He said they were keeping an open mind about what happened and had been speaking with family members.
"We will continue to approach and speak with witnesses and family members as the investigation progresses and are hoping that all persons involved will cooperate and provide any information they may have that helps us understand what has happened to the baby."
Police were seeking information from family members or witnesses who had any interactions with baby Kween in the two weeks prior to her death.
Verry said police were aware of "a number of different theories from the wider family" as to what occurred and he encouraged anyone with information to consider speaking with police in confidence.
"Information can be provided in person at a local Police station or through our 105 reporting line," he said.
"Please reference file number 230714/4866.
"Information can also be provided anonymously via Crime Stoppers on 0800 555 111."