Mr Stilton said the woman had been walking along the left side of the road, which is a 100km/h zone, when she was hit.
He believed the woman had been knocked over some time between 11pm and 11.30pm.
Police were treating the incident as a hit and run, and were urging any witnesses to the incident to come forward.
"The driver will know that they've hit someone, so we'd like them to come forward."
Mr Stilton said there was absolutely no way the driver could not have noticed they'd struck the victim.
He believed the woman had family living in the Normanby area, to whom she may have been walking.
"She's got a head injury so she's a little bit unsure about what she was doing out there, it's possible that she'd been drinking and got confused about where she was going."
No witnesses had come forward yet, but anyone with information should call the Hawera police station on 06 278 0264.