Activists are expected to protest the demolition of Anzac Hall from 2pm on Monday.
The flattening of the 20-year-old building will make way for a new gallery space, with the Australian War Memorial set to undergo a $500 million expansion.
The war memorial said work crews were on site from Monday morning, and machinery was expected to be on and off throughout the day.
Last week, 27 trees along Treloar Crescent were chopped down to help make way for the new works.
The removed trees will then be taken to a Canberra green-waste facility for mulching, the war memorial said.
During the process, 140 trees which were planted nearly a century ago, will be felled.
The war memorial has said it had plans to replace all of the felled trees with newly planted ones, adding an extra 70 to the site.
The works have received heritage and parliamentary approval and the green light from the National Capital Authority.
