A search operation for a grandmother missing near Melbourne has been expanded, with police hoping she's still alive after potentially four nights in the wilderness.
Susan Shaw, 67, hasn't been seen since police stopped her walking along Mount Donna Buang Rd at 1.40am on Friday morning at Warburton, east of Melbourne.
Ms Shaw assured officers she was out for a late-night walk to Warburton's Rainforest Gallery, but a 120-personnel strong search operation has yet to find any trace of her.
Senior Sergeant Peter Muys said police, rescue specialists, and SES and CFA volunteers have broadened the search area on Monday, moving deeper into the bush.
Crews remain "optimistic" about finding her safe and well, he says, despite concerns she might not have food or water.
"The one thing to take into account is that the weather hasn't been extreme," Sgt Muys told reporters on Monday.
"We've had fairly mild nights. So we believe it's entirely possible that Susan could be moving in and around the area.
"Obviously as time goes by the lack of food or water or food - if she's not got access to that - does become an increasing concern."
A local, Ms Shaw's knowledge of the dense and steep terrain and relative fitness is fuelling their optimism.
She was wearing a blue/green cardigan, jeans and bright pink boots when police last spoke with her.
Sgt Muys says a camper, who is believed to have set up a tent in the area on Friday, may hold the key to finding Ms Shaw.
"We believe there was someone where she was last seen and we'd appeal to that person to make contact with police as soon as they can because it's quite likely they were the last point of contact," he said.
Crews are expected to continue searching until nightfall, before resuming at first light on Tuesday if Ms Shaw remains missing.
