A three-year-old boy who went missing in the Australian bush four days ago has been found safe after a search.

Anthony "AJ" Elfalak was spotted by police helicopters on Monday, drinking water from a creek on his family's property in rural New South Wales.

The little boy, who has autism and doesn't speak, had been last seen at the house on Friday.

His family had feared that he had been abducted.

But rescuers found AJ on a riverbank about 500m from his house on the vast property in Putty, in the state's north.

In footage shared by New South Wales Police, rescuers can be heard saying "I've got the boy".

Authorities said AJ had suffered a few scrapes to his lower legs and was found drenched in wet clothes, but was otherwise in good health.

His father, Anthony Elfalak, called it a "miracle".

More than 100 officers and volunteers spent days scouring the bush for his son. They had earlier passed over the area where he was ultimately found.

"He has been bitten by ants and he has fallen over but he is alive. He is alive," a jubilant Mr Elfalak told television crews.

"I know I was acting frantic, but no-one can understand what it's like going through what we went through. I feel incredible.

"My leg, my hips, my ankles, I can't walk. I have been in the bush for four days with no sleep. We didn't stop."

Local media showed scenes of family members cheering and rejoicing when they heard the good news.

Prime Minister Scott Morrison also expressed relief, tweeting that he was "glad to hear he's safe".

"I can't imagine how traumatic this experience has been for AJ and his parents," he said.

It's unclear why the boy had wandered off, his parents said.

AJ had been playing with his brothers in the morning on Friday, and usually stuck close to his mother.

Police seized a white vehicle on Sunday, in the belief that they were investigating a kidnapping case. (BBC)

Update news