If you are a resident in Australia for tax purposes, you are required to declare any income from any country. You are breaking the law if you do otherwise- bank accounts or not.This is not true if you keep your funds in Hong Kong. Anyone is allowed to open bank account in Hong Kong, you do not have to be a resident or citizen there.
ATO has firm requirements for being a resident for tax purposes. It's not enough to leave the country for 12 months. The last time I looked (that was a while ago) you had to prove that it was your intention to stay away permanently.