The Privet Hawk Moth – a spectacular caterpillar and an impressive moth! The camouflage is brilliant among leaves. I’m uncertain which of these similar species the photo depicts; the Privet Hawk Moth P. menephron, or the Privet Hawk Moth P. casuarinae? Food plants include Privet (no prizes there!), Jasmine and a variety of other garden plants. In some districts the caterpillars can become pests. Pupation occurs underground. Adult Hawk Moths are superb fliers and voracious nectar feeders, hovering before a flower to feed, rather than alighting. This photo comes from a garden in Euroa.
Here’s Hawk Moth information from Brisbane Insects website.
And a bit more from the Australian Museum.
Perhaps you can work out which species it is.