New Zealand police on Thursday confirmed that human remains found in two suitcases bought at an Auckland auction were of two primary school-aged children, with officers vowing to find those responsible.

Detective Inspector Tofilau Faamanuia Vaaelua said the bodies were likely to have been in storage for several years and the victims are thought to have been between five and ten years old.

The children were concealed in two suitcases of similar size, he said.

"The nature of this discovery provides some complexities to the investigation especially given the time lapsed between the time of death and the time of discovery," Vaaelua added.

The remains were only discovered when a family brought a trailer-load of items being sold in bulk from a storage unit. 

Police reiterated that the family concerned are not connected to the homicide, but are "understandably distressed by the discovery" and they have asked for privacy, Vaaelua added.

Household and personal items found alongside the suitcases are helping provide clues to identify the victims.

Both the storage unit and property where the suitcases were taken to have been thoroughly examined by forensic experts.

Vaaelua also revealed that police in New Zealand are working with international criminal agency Interpol in their investigation.

The relatives of the victims are thought to be in New Zealand.

The children had not yet been identified and Vaaelua said he felt for their families, who might not be aware they were dead.

"A lot of us (in the police) are parents and we have a job to do and we're doing our very best to identify the victims," he said.

"What I can say is we are making very good progress with DNA inquiries.

"The investigation team is working very hard to hold accountable the person or persons responsible for the death of these children."

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