The search will resume for the 11-year-old boy missing near Lake Eildon since Good Friday.

The search for an autistic boy missing in a Victorian national park has entered its fourth day.

Eleven-year-old Luke Shambrook went missing in the Fraser National Park on Good Friday.

Rescue efforts resumed at first light on Monday, with fresh hope after a possible sighting.

A lone boy was spotted in the bush late on Sunday.

'A family that was driving in the Devils River area have told police that they saw someone matching Luke's description,' a Victoria Police spokeswoman said.

'So, they have extended the search to cover that area.'

Campers are helping rescue teams involving the air wing, dog squad, local police and SES volunteers in the search of thick bushland.

The state's SES service has asked the public not to head to the area to help with the search.

'While we understand that everyone is worried about Luke, we ask people not to head to the area to help out,' a Sunday night post on Facebook said.

'At this stage, more people will only complicate the scene.

'Help will be requested if needed.'