A man has appeared in the Whangarei District Court charged with assaulting a child on Tuesday.
The 17-month-old girl, who has head injuries, is in a critical but stable condition in Starship Hospital in Auckland.
The accused man, 39, has been granted interim name suppression and was remanded in custody for three weeks.
Police are carrying out a scene examination at the house where the child was hurt and are interviewing family members and neighbours.
The girl is the second critically injured Northland child to be taken to Starship Hospital in the past few days.
A two-year-old Kaitaia girl died in a separate incident. That girl's mother is charged with assault.