They hoped to arrive at the base of the mountain by Thursday evening.
The Civil Aviation Authority of the Philippines (CAAP) said the plane’s wreckage was on the western side of the volcano, about 1,070m to 1,200m above sea level.
“It’s a very difficult terrain,” said Albay disaster officer Cedric Daep, warning the retrieval operation could take longer than a day.
“It’s steep and there are ridges where only one person can climb at a time.”
Manila-based Energy Development Corporation said previously that it owned the plane. The Australians were technical consultants for the renewable energy company.
“Our heartfelt sympathies go to their families and friends during this difficult time,” company president Richard Tantoco said in a statement.
The wreckage was spotted on Sunday, but rain, clouds and the risk of a volcanic eruption hampered efforts to reach the crash site.
A rescue team, including veteran mountaineers, began making the steep climb on foot on Tuesday.