Necessary to carry passport at all times? (Sydney)

Hi everyone

Is it required to carry your passport in Australia everywhere you go? In Belgium (where I come from), it is compulsory to be able to proof your identity at all times - and you do get a fine if you cannot!
In Denmark (where I lived for 12 years), there is no such requirement unless you are driving, and then obviously you need to be able to present your driving's license.
I have tried to get an answer to this question, but without any luck so far. Hopefully anyone of you can help out :-)

Best regards
Nathalie