The child was assessed and treated at the scene before being transported to Whanganui Hospital in a critical condition.
Police said the vehicle involved was described as a small light blue hatchback and asked anyone travelling in the area at the time, including the surrounding streets of Cornfoot, Manuka and Polson St, to contact police if they saw the vehicle.
Residents were also asked to check any CCTV cameras they have and pass on the footage to police.
Police understood the driver of the vehicle was likely shocked and distressed by the incident, but they were urged to do the right thing and come forward.
Members of the public with information on the incident can contact police by calling 105 and quoting reference number 231112/8246.
Finn Williams is a multimedia journalist for the Whanganui Chronicle. He joined the Chronicle in early 2022 and regularly covers stories about business, events and emergencies. He also enjoys writing opinion columns on whatever interests him.