"There's nothing at all that's been located today that is in any way connected to the disappearance of the Beaumont children. Sadly, this means for the Beaumont family we still have no answers," Detective Superintendent Des Bray told reporters at the site.

Friday's excavation took place at the Castalloy factory, which was once owned by businessman Harry Phipps. He died in 2004.

His house was only 250 meters away from where the trio were last seen alive and the physical appearance of Phipps matched the description given by other witnesses who had claimed to have seen the children in the company of a tall man in his late thirties with "fair to light brown hair", a tan, medium build and a thin face.

Phipps came to police attention in 2007 when a book was published that suggested he might be a credible suspect, but was not taken seriously until two men came forward claiming to have been paid by Phipps to dig a trench at his factory site as teenagers.

Bray said police had previously searched the property in 2013, based on the information provided by the two men, but found nothing.

The latest search efforts came to fruition after a forensics team from Flinders University working with local television station Channel 7 revisited the Castalloy factory to re-examine the site with ground penetrating radar and found an "anomaly" that matched the size of the hole dug by the two men.

Friday's dig uncovered some bones which were quickly discounted as belonging to animals.

Bray said authorities will continue to investigate the case.

"We will always do anything humanly possible to locate the Beaumont children and take them home to their family," he said.