The 4-month-old baby found dead in Waiuku yesterday was sleeping with her mother in a van.

They were sleeping in the vehicle as their house was being renovated.

But a post-mortem examination this morning was inconclusive as to the cause of death.

Police are looking into whether the temperature inside the vehicle could have contributed to the baby girl's death.

MetService meteorologist Tom Adams said temperatures at Auckland Airport reached a high of 20.6C at 3pm. He said the temperature in Waiuku would have been similar.

Acting Detective Inspector Colin Higson said the family have asked to grieve privately.

"Understandably, this is a very stressful time for the baby's family and her death is an absolute tragedy for them.

"Although this is an ongoing investigation, it is a timely reminder to all of our community of the dangers of leaving children in vehicles during the warmer months."

Police urged people to take action if they see a baby or child unattended in a vehicle on a hot day and call police immediately.