A woman ran to her neighbour's house to find a critically ill baby going purple and his eyes rolling in his head yesterday.
The baby was then rushed to Waikato Hospital but had to be airlifted to the Starship children's hospital with head injuries following what police say was a domestic-related incident.
The Waikato field crime manager, Acting Detective Inspector Mark Greene, said police had arrested a 32-year-old man.
He will appear in the Hamilton District Court today to face a charge of assault on a child.
The baby boy, understood to be about 9 months old, was taken to hospital by ambulance at 11.35am after the incident at a York St home in Hamilton East.