Expired Visas
Under the Migration Act 1958 (the Act), if your visa expires while you are still in Australia, you become an 'unlawful non-citizen'. The Act provides that if you have no entitlement to remain in Australia, you may be detained and removed from Australia as soon as practical.
Compliance officers locate people who have become 'unlawful non-citizens' or who are commonly known as 'overstayers'. If there is no legal entitlement for them to remain, they are expected to depart Australia.
If you become aware that you are an 'unlawful non-citizen' you should take immediate steps to regularise your status (you may wish to seek legal advice), or you should make immediate arrangements to depart and contact the compliance section of your nearest departmental office with evidence of your departure booking.
If you are eligible, a departmental officer will grant you a bridging visa to give you lawful status for a short time. The bridging visa provides an opportunity to organise your personal affairs before departure or to lodge an application for a new visa, if this is an option for you.
See: Bridging Visa
Further information:
Managing the Border: Immigration Compliance (Chapter 5 - Dealing with Overstayers)