South Australia Police are “hoping for the best” as they recommence a long-running search for the missing Beaumont children after a recent breakthrough in the 52-year-old cold case prompted 46 fresh tips from the public.

A dig commenced at 8am on Friday at an Adelaide factory site in North Plympton as part of a renewed effort to locate the bodies of Jane, 9, Arnna, 7 and Grant, 4, who went missing from Glenelg beach on January 26, 1966.

Attention is focused on a small section of ground at the factory site where geophysical tests by Flinders University in January revealed the possible presence of a large hole dug there around the same time the three children went missing in 1966.

By late afternoon, the excavation had unearthed animal bones — thought to be those of a cow or horse — but no sign of the missing children.

“We’re now into the area of interest. If we break it up into two parts, on the eastern side, we are right down to about 2.3 metres, we’re clearly into virgin soil and we’re not finding anything at this point,” said Detective Chief Inspector Greg Hutchins.

“In relation to the western side, we’ve found a number of non-human bones from a large animal, similar to a horse or cow, we’ve also found quite a bit of rubbish, so clearly we’re in disturbed soil.

“The process now, they will shortly move to the western side of the hole, I’m not sure how long that will take, but as there is rubbish there, it may take a bit longer than it’s taken to get to the bottom of the east side.”

Detective Chief Inspector Greg Hutchins cautioned that there are innocent explanations for the anomaly those tests uncovered but it could also be a major breakthrough in Australia’s most enduring cold case.

“We have our fingers crossed, we hope for the best but we do want to temper expectations,” he told reporters at the site on Friday.

“Clearly we have an anomaly which we need to investigate,” he said.

“This is a slow and methodical search … I can’t have a guess what they might find but now it’s methodical digging, looking.

“The good thing is it’s very sandy and it’s very easy for them to see or identify any strange object, thing, rubbish, clothing.

The dig is “methodical’ and proceeding with deliberate slowness, police say. Photo: AAP

The site was previously owned by businessman Harry Phipps, a person of interest in the case who died in 2004.

The anomaly suggested a hole had been dug at the site which, when taken with evidence provided by two brothers that they had dug a hole there for Mr Phipps in 1966, marked a major breakthrough in the long-dormant case.

The resultant Channel Seven coverage has proven helpful to the investigation itself, with SA police revealing it had received 46 new calls to Crime Stoppers since January 22 thanks to media attention.

“I wouldn’t necessarily say its unusual [the number of new reports] but what we would say is that it’s certainly encouraging and we welcome that number of reports,” an SA Police spokesperson told The New Daily.

Police will assess the credibility of each individual phone call, but the nature of the tips remains confidential.

Missing Beaumont children excavation: https://t.co/c0ikTAK4k1 via @YouTube

— South Australia Police (@SAPoliceNews) February 1, 2018

Friday’s dig is expected to excavate up to three metres below ground and will be overseen by police from Major Crime and Forensic Response, an anthropologist from SA Forensic Services, a professor from Flinders University and members of the SES.

The excavation site is around 50 metres from where police have previously searched and the location is consistent with where the brothers had said they dug a hole when they were only boys.

“That analysis identified a small anomaly in the middle of the block consistent with where the brothers said they had dug, but there was no obvious reason for that anomaly,” Detective Superintendent Des Bray said.

“There could be an innocent explanation or it could well be the hole they dug.

“They are not suggesting it was a grave, but certainly it was sufficient to merit further investigation and that’s what we’ve committed to do.”