Police said the man allegedly slipped inside Alpha Archaeology on Union Street in Ascot Vale, Melbourne and filled his bag with artefacts "of cultural significance" at 3.42am on February 2, 2024.

Sergeant Robert Weir said the crime appeared to be opportunistic and the man grabbed pieces that were "easily accessible" after leaning on the front door and finding it unlocked.

Archaeologist Madeleine Van Ewyk said she was "absolutely gutted" to discover the artefacts had allegedly been stolen.

Alpha Archaeology were conducting tests on the artefacts that are "highly significant to an Aboriginal group in Melbourne", she said.

The company had the items in their care for around a year and a half, Ms Van Ewyk said.

She declined to elaborate on the cultural significance of the items or the Indigenous group to which they belong.

"For the purpose of research and further repatriation processes, it's really important for these artefacts to come back."

The alleged thief opted to take the artefacts instead of the business' electronics.

Ms Van Ewyk said the man will likely struggle to find a buyer for the items.

"It is incredibly difficult to sell them on the Australian market," she said.

"[It'd] be great if you could just give them back."

Police describe the man as being Causasian, around 40 to 50-years-old with "scruffy hair".

Anyone who witnessed the incident or has information is urged to contact Crime Stoppers on 1800 333 000 or submit a confidential report online at www.crimestoppersvic.com.au