One of Perth's oldest cemetery sites is set to give way to the march of development — in the form of apartment towers, shops and office blocks — but not before revealing precious information about the city's formative years.

Key points: An estimated 400 bodies are buried on the historic East Perth site

An estimated 400 bodies are buried on the historic East Perth site Developers bought the land in 2018 under condition remains be preserved

Developers bought the land in 2018 under condition remains be preserved It was a site for mainly Presbyterian and Chinese communities

Tucked behind the old Perth Girls' School, once part of the East Perth Cemeteries grounds and later developed into school playing fields and a Department of Transport licensing centre, the Bronte Street site's secrets are lost in history.

There are no surviving records of who or exactly how many people were buried there until 1916, with the only clues pointing towards the Presbyterian and Chinese communities.

The 6,265 square metre site was acquired from the WA Government in 2018 by a private syndicate headed up by Australian Development Capital and the Warburton Group, who plan on creating a new civic precinct in the area in conjunction with the revived Perth Girls' School and another Bronte Street property.

A condition of the sale for the Bronte Street land was that any human remains would be exhumed and reinterred, and work to bring up the hundreds of bodies from unmarked graves is about to begin.

The main East Perth Cemeteries site to the east of Plain Street will not be affected.

The unmarked graves are part of the East Perth cemeteries grounds. Bodies in the area pictured will not be exhumed. ( 720 ABC Perth: Emma Wynne )

Australian Development Capital executive director Rod Hamersley said the excavation project was due to be completed in the first quarter of 2020, but admitted there were unknowns at play.

"All we've been able to do at this point is do some ground-penetrating radars to understand anomalies below the surface, but that could be any form of material, whether it be human remains, or rocks, stumps, the like," he said.

"I'm not sure we had hesitations [buying the land], but we certainly spent a lot of time understanding the sensitivities with the site, particularly given the Government took the site to market with the condition that the private sector complete the excavation program."

Relatives sought for exhumed remains

National Trust of WA manager of interpretation and collections Sarah Murphy said it was an unusual opportunity to find out more about the site, burial practices and the broader East Perth Cemeteries.

"There are mysteries throughout that whole site," she said.

"A lot of the early records just weren't well kept, or they were kept by the undertakers and hadn't survived. The records are patchy."

The broader East Perth Cemeteries site is home to a number of different cemeteries, which were all once managed by different churches.

The cemeteries were closed to new burials in 1899, with concerns the area was becoming too full, worries over the spread of disease and more people coming to live in the East Perth area.

Ms Murphy said the Royal Western Australian Historical Society was one of several groups that pushed for the cemeteries to be preserved in the 1950s, but it was too late for the Presbyterian, Jewish and Chinese cemeteries, which had already been relinquished.

The Bronte Street site where the apartment complex will be built. ( ABC News: Hugh Sando )

The Jewish cemetery is now managed by the National Trust as part of the larger East Perth Cemeteries site and has become a memorial area with records available.

Anyone with a potential key to the missing information about the Presbyterian and Chinese cemeteries was urged to contact the National Trust.

"If someone can come to us and say, 'look, I know that my ancestor was buried here, here's the death certificate', or, 'we have this piece of correspondence', that helps us build up a picture of exactly who was buried there," Ms Murphy said.

"That opens up great opportunities for us in terms of sharing more stories."

Memorial garden planned at Karrakatta

A specialist team of archaeologists and forensic anthropologists would carry out the upcoming excavation work and analyse the remains, with a profile — including estimated age at death, biological sex, stature, ethnicity and any indicators of disease or trauma — to be produced for each individual.

Personal items like rings, necklaces and watches found with skeletal remains would be cleaned, photographed and reburied with the respective remains.

The remains would then be taken to Karrakatta Cemetery and reinterred in an area to be known as the East Perth Cemeteries Memorial Garden.

The Bronte Street site would not be open to the public during the process out of respect for the deceased and any potential living relatives.