Frantic search for missing three-year-old last seen on Friday in the NSW Hunter Valley

The search for a three-year-old boy missing for more than 24 continues in difficult terrain, with cops saying every minute is crucial.

A full scale search is underway for a boy who went missing on a property in the Upper Hunter.

A three-year-old boy is still missing more than 24 hours after he was last seen with police refusing to rule out foul play.

Emergency services were called to a rural property on Yengo Drive at Putty in the NSW Hunter Valley about 12.30pm on Friday when the toddler went missing.

The boy, called AJ, who has autism and is non-verbal, could not be found after he was last seen about 11.45am.

“Police are absolutely looking into every angle possible in relation to AJ’s disappearance,” Hunter Valley Police District Superintendent Tracy Chapman told reporters on Saturday.

AJ has been missing since Friday.

When questioned about whether police were investigating anything “sinister” about the disappearance she said they were looking at all angles.

“Our focus is very much around our search and trying to locate AJ but we do have an investigation underway,” she said.

More than 130 people who are trained in searching are on the ground searching in “difficult terrain” to find the missing boy.

The search continues for AJ more than 24 hours after he disappeared on the property. Picture: David Swift

A dam had been drained on the property on Friday and police divers searched it but had not found anything, Superintendent Chapman said.

“Obviously the terrain is very, very difficult, we’re in a rural setting,” she said.

They had also searched other waterways and dams with SES volunteers combing the bushland for AJ.

“Really every minute is important so our priority is to find AJ as quickly as we can.”

Divers search waterways for any trace of the missing boy. Picture: David Swift

Mounted police join the search for three-year-old AJ who has gone missing from a rural property in Putty. Picture: David Swift

Police said there were sufficient emergency services and trained personnel at the scene with the public urged not to encroach on the rescue efforts.