Police say they have identified a car that may have been involved in a suspected hit-and-run on the Waikato Expressway.
They said a member of the public called at about 3am to say a body was lying on the northbound lane of the road near Mercer, about 70 kilometres north of Hamilton.
Inspector Kerry Watson said several passing motorists stopped and used their cars to protect the woman's body until the police arrived.
Senior Sergeant Ian Brenchley said officers suspect she was the victim of a hit-and-run.
The northbound lane was closed while serious crash investigators examined the road where the body was found. It has since been re-opened.