The search for a teenager with non-verbal autism who went missing continues more than 24 hours after he was last seen in regional Victoria.
Hundreds of people are racing to find William Callaghan,14, who became lost in steep and rugged terrain on Mount Disappointment about 2.20pm on Monday.
William became separated from his family wearing just blue trackpants and a hoodie ahead of a night where temperatures dropped below zero.
Acting Inspector Christine Lalor said the youngster been walking to the summit with his family when he raced ahead.
William Callaghan was last seen on Monday afternoon. Source: Supplied
Tuesday's clear, sunny sky kept hopes high of finding him after an air-and- ground search started on Monday afternoon.
But with another chilly night coming, fears for the boy are growing.
"It's going to be another cold evening again, hence ... it's vital that we try to find William before nightfall," Inspector Lalor said.
"(His parents) are holding up as well as can be expected."
Search and Rescue Squad Senior Sergeant Greg Paul told reporters on Tuesday they were fighting against time, but remained hopeful.
The weather bureau expects the temperature on the exposed mountain to drop to zero degrees and -3C in the valleys overnight.
"It's quite life-threatening weather, but we have had people survived several nights in these weather conditions as well," he said.
"Luke Shambrook, six years ago ... we found him on day five, he was alive and he's alive today."
A mix of four-wheel-drives, people on foot, motor bikes, horseback and those in the air are involved in the search.
More than 200 volunteers joined about 150 police and emergency services who are looking for William.
Senior Sergeant Paul said the area had very thick bush from bushfire regrowth and it hampered searches, given the undergrowth.
But they were "giving it our best effort" to search the steep terrain.
"The only advantage is ... there is an opportunity to stay a little bit warm if you can snuggle up in the undergrowth," he said.
William went missing without food and water and could have covered a lot of distance by now, police said.
He is very energetic and food-focused, with police believing he may have walked into a house to help himself to food, or tuck himself into a bed.
"William doesn't verbalise so if anyone finds him the best way to communicate with him is to be patient and calm," Acting Inspector Lalor said, adding William taps his chest to communicate.
"If anyone in the area could check their homes, check their beds and any out houses to see if William is in those locations."
