No new evidence has been found on the third day of the renewed search for missing four-year-old Gus Lamont, with efforts cut short due to extreme heat.

More than 100 personnel, including the Australian Defence Force and SES were out in the landscape surrounding Yunta from first light this morning, searching for fresh clues to try and find out what happened to the boy who has been missing since September 27.

Today marked day three of an extended search under the name Task Force Horizon to try and find Lamont, with the focus on a 5.5km radius around the remote homestead from where he went missing.

Missing four-year-old Gus Lamont. (South Australia Police)
Gus was last seen about 5pm on Saturday, September 27 at his family’s homestead Oak Park Station in remote South Australia, about 40km south of Yunta.

Taskforce Horizon consists of 12 specialists who will analyse information and suggest different areas to search.

Police have said they believe they will finish the search of that radius by tomorrow.

Search efforts today were stopped at midday as temperatures hit 37 degrees in the area.

Police search for missing four-year-old Gus in outback SA (9News)
Police insist the case is still a missing persons investigation, though major crime detectives are monitoring the case and are keeping all lines of inquiry open.

“We are dedicated to making sure we do everything we possibly can to bring Gus back to his family,” South Australia Police Commissioner Grant Stevens said on Tuesday.

“We are searching in quite unusual terrain, it is a significant effort… we’re exhausting every opportunity to recover Gus.”