Hastings police say it could be several weeks before it is known what caused the deaths of mother and her two young daughters in the coastal Hawke's Bay settlement of Haumoana.
The bodies of Melissa Dorward, 31, and her children, Keira and Ellah Watson, aged four and two, were found by a family member at their home on Sunday morning.
Detective Senior Sergeant Dave de Lange said on Monday post mortems were still being completed in Wellington.
He said police are working closely with a patholgist and waiting for the results of toxicology and forensic tests.
Mr de Lange said it is likely the case will be referred to the coroner once the police investigation is finished.