A new police search will be made for the Beaumont children at an Adelaide factory site once owned by a man police have investigated as part of the case.

Key points: Police will excavate a new area of the Castalloy factory in search of the Beaumont children

Police will excavate a new area of the Castalloy factory in search of the Beaumont children The site was previously searched in 2013

The site was previously searched in 2013 The Beaumont children went missing on January 26, 1966

The three children went missing from Glenelg beach on January 26, 1966.

Adelaide businessman Harry Phipps, who died in 2004, once owned the North Plympton site on which police will again focus their investigation.

The Beaumont case has been subject to a review by SA Police's Major Crime Investigation Branch in the past year.

At the same time, Channel 7 conducted its own probe into the disappearance of Jane, 9, Arnna, 7, and Grant, 4, and made police aware of geophysical test results and new information from witnesses.

A sketch of the man witnesses said they saw with the Beaumont children the day they disappeared. ( Supplied: SA Police )

As a result police will excavate another part of a North Plympton factory site, which is now Castalloy, in the next few weeks.

The dig follows an earlier excavation at the property in 2013 in which nothing was found.

Police used ground-penetrating radar and excavated a one-metre-squared section of the site, but no bodies were found.

Businessman who owned factory site investigated before

At the time the children went missing, several witnesses told police they had seen them with a tall, tanned, thin-faced man with short, blond hair.

Channel 7 reported Mr Phipps' son told authorities he saw the Beaumont children in the backyard of his home on the day they vanished.

Police searched a part of the Castalloy factory site in 2013.

In 2013, The Advertiser reported Major Crime detectives had admitted Mr Phipps was not a suspect in the case.

At the time police said allegations implicating him had been investigated and discounted and there was no information that would justify the excavation "of any property".

Over the years, many suspects have been suggested, investigated and discarded by police.

A reward of $1 million remains on offer by the State Government and police are calling on anyone with more information into the Beaumont case to come forward.