The search for a missing preschooler is being scaled back after police concede the boy is likely dead after wandering away from an outback homestead.

August, known as Gus, went missing from his family's sheep station in the remote South Australian mid-north on Saturday afternoon.

The only trace found of the four-year-old was a tiny footprint in the dirt about 500 metres from the family homestead, despite an extensive search involving police, Defence Force personnel and large numbers of volunteers.

"Whilst we've all been hoping for a miracle, that miracle has not eventuated," SA Police Assistant Commissioner Ian Parrott told reporters on Friday.

"This is clearly now what appears to be a very tragic set of circumstances."

No significant evidence was found to allow emergency services to

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