Glabrous annual to 3 m high; stems 4-angled ± winged.
Maybe some kind of primrose-willow? The leaves are curlier than photos I’ve seen of them, so I’m not sure.
large flower narrow leaf
This plant is in the Family of Asteraceae because of the characteristic inflorescence. This is identified as Ageratina adenophora as the inflorescence is white, without ray flowers, and has a cluster of long hairs (pappus). The shape and phyllotaxis of the leaves match the description in 'Field Guide to the Native Plants of Sydney' (Les Robinson). It also cannot be Ageratina riparia due to this observation being a large shrub, rather than a sprawling shrub.
It's some sort of vine.