A 15-month-old Greymouth boy died at Auckland's Starship Hospital last Thursday due to a bleed on his brain, police say.
An investigation was now taking place to establish how the young boy sustained his injuries.
Detective Senior Sergeant Keno said 15-month-old Leith Allan Hutchison was taken to Grey Base hospital early last Tuesday morning by a member of his family.
He had stopped breathing and was in cardiac arrest, Mr Keno said.
"Medical staff managed to resuscitate and stabilise him and he was moved by air ambulance to Starship hospital later that day for specialised medical care."