Expensively.

China to China? Seems a bit like coal to Newcastle.

From what has been said on the boards -

Pack with something like scrunched up newspaper inside.

LOOSELY wrap with bubblewrap. Bubblewrqap can contract when heated, so you need to allow for that.

Put in a box and pack the gaps with newspaper or packing peanuts.

Put in another box and do the same as the first one.

DO NOT put anything anywhere that implies the contents are fragile.

Be aware that Australia Post expect any parcel to be able to withstand having 22kg dropped on it from waist height.