As crews scour the area around Kendall for a sixth day, they have come to the grim realisation the search-and-rescue mission that began on Friday morning, and which has drawn hundreds of people to the tiny community, has most likely turned into a recovery operation.

Superintendent Paul Fehon said police still had no idea whether William, who was last seen wearing his favourite Spider-Man costume, had wandered off from the front yard of his grandmother's house on Benaroon Drive on his own, or whether "other forms of human intervention are involved".

"As days go on, people are out there and trying to come to terms with survival in the bush," he said.

But if he had wandered away, the likelihood of the boy surviving on his own in the thick bushland surrounding the property was non-existent, Superintendent Fehon said. "Experts have advised us they cannot substantiate that, at this point in time, survival could exist."

However indigenous tracker and bush survival expert Jake Cassar, who has joined the search, said it was "absolutely possible" William might be alive.

"I've known young people to go up to a week without water before the body breaks down," he said. "The weather here has been quite temperate but the issues will be the asthma and that he wouldn't have a great deal of energy."

He was concerned by footprints he detected on Tuesday from an "enormous" wild dog in the thick bushland nearby.

Superintendent Fehon said William's family were under immense pressure, and felt numb after the boy's disappearance.

"They are very grateful of all the search efforts of everyone that's out here ... in regards to the efforts of trying to bring young William back," he said.

He would not comment on information Fairfax Media received about a man asking staff in a local shop for directions to Benaroon Drive on Friday, before William went missing.

"We're grateful of all the information that's been provided to us at this point in time and we are following up on all those leads of information," he said.