The discovery of a small footprint is providing a glimmer of hope before the search for a preschooler on an outback homestead becomes a grim recovery operation.
Four-year-old August, known as Gus, disappeared from his family's sheep station in the remote South Australian mid-north on Saturday afternoon.
Alone in searing temperatures and without food or water, authorities' best-case scenario is Gus has crawled into shelter and is waiting to be rescued from the property near Yunta, about 300km north of Adelaide.
In a significant development, a footprint was found on Tuesday night, buoying tireless searchers who have worked day and night to bring the preschooler home safely.
"We had a little bit of a breakthrough yesterday where we found a footprint about 500 metres away from the property," Superintendent Mark Syrus told ABC Radio on Wednesday.
"It has been pretty windy, but it's quite a prominent footprint," he said.
"We can positively identify that it's from a child and it's a very similar boot pattern to what Gus was wearing when he went missing, so that's a pretty significant find for us."
However, police have also prepared the family for the worst after five days of searching.
"This is a young boy without food, water, shelter for that period of time, so it is going to be pretty tough on that little lad," Supt Syrus said.
"We're preparing the family for the fact that we may be moving from a search effort to a recovery."
Until then, a specialist tracker with deep knowledge of the terrain has been called in to help with the search.
Gus's distraught family broke their silence on Tuesday, saying they were "struggling to comprehend what has happened" to the youngster.
"Gus's absence is felt in all of us, and we miss him more than words can express," Bill Harbison said on the family's behalf.
"Our hearts are aching and we are holding on to hope that he will be found and returned safely."
The adventurous boy had been playing in the sand near the family homestead when he disappeared.
Despite frantic efforts stretching for more than three hours, no trace could be found.
Extensive ground searches involving State Emergency Service volunteers on trail bikes, all-terrain vehicles, dogs and a drone have been carried out, while helicopters, police divers and mounted officers have also been involved.
Police don't believe the disappearance is suspicious.
Gus has long, blond, curly hair. He was last seen wearing a grey sun hat, a cobalt blue T-shirt with a yellow minion on the front, light grey long pants and boots.
