Blistering heat is hampering the South Australian search for four-year-old Gus Lamont on Thursday.

It comes as new details surface about what the missing boy’s family were doing when he vanished from their outback property near Yunta 19 days ago.

It’s the third day of renewed search efforts, and temperatures reaching 36C are expected to scorch the rural area 275km northeast of Adelaide, as about 100 search team members walk up to 25km from sunrise to midday.

No evidence has been found of the little boy who was last seen playing on a mound of dirt outside his grandmother’s homestead about 5pm on September 27.

The little boy was left unsupervised for 30 minutes, police were told.

During that time, Gus’s grandmother had been inside, watching his little brother, Ronnie, 7NEWS understands.

The boy’s mother and his other grandparent were 10km away, tending to the station’s sheep.

The boy’s father was not on the property at the time.

Gus’s grandmother discovered the boy missing after calling him inside about 5.30pm.

Family called police to report the boy missing three hours later.

Nearly 500km2 have been scoured by rescue and recovery teams in what is now one of the largest land searches in the state’s history.

There is no evidence at this stage to suggest any foul play.

The search is now being considered a recovery mission, as harsh conditions and passing time make the young boy’s survival evermore unlikely.

Link: https://7news.com.au/news/gua-lamont-search-new-details-emerge-of-missing-boys-last-night-with-family-c-20365163