The two deaths brought the provisional national weekend road toll to five late last night, the worst since 2012.
Today, police said a number of vehicles and other places of interest were being examined as part of the investigation, and police were being assisted by ESR.
A post-mortem examination had been carried out.
Police remain tight-lipped about how the woman died and detectives from Invercargill were yesterday trying to piece together the hours which led up to her death.
Last night, police would not discuss the details of her death or confirm whether they had spoken to the driver involved.
A St John spokeswoman confirmed the woman died at the scene.
Senior Sergeant Brian Benn said police wanted to speak to anyone who saw a woman wearing a blue jacket and pink shoes walking along the highway between 9pm Sunday and 1am yesterday.
He would not discuss the woman's details, including her age.
Police were awaiting pathology reports before discussing whether alcohol was a factor in the incident.
The road was closed until early afternoon yesterday as Invercargill CIB and serious crash investigators pieced together the incident.
Anyone who travelled between Invercargill and Bluff between 9pm on Sunday and 12.50am yesterday was asked to contact police on 03 211 0400.
In the other incident, an Invercargill woman died after smashing her car into a concrete wall and store window of the Farmers building in Dee St after what is understood to be a medical event.
Police would not confirm that yesterday and said the investigation was ongoing.
Senior station officer Deane Chalmers, of Invercargill, said it had been a "pretty rough night" for firefighters who attended both incidents.
The Invercargill woman's body was removed from the car about 11am and the car was removed from the building about 15 minutes later, he said.
Southern district road policing manager Inspector Tania Baron said the fatalities were disappointing for police.
"Our thoughts and hearts go to the families of those involved," she said.
