It is a State offence to wilfully trespass in any place and neglect or refuse to leave that place after being warned to do so by the owner, occupier or a person authorised by the owner or occupier (section 9(1)(d) Summary Offences Act 1966 (Vic) ). The maximum penalty is $2500 or six months' jail, although the penalty is usually a small fine. However, every case is different so you should seek legal advice about the penalty you may face.
If you enter onto another person's land without their permission, you will be trespassing. If you deliberately or carelessly do something that directly causes interference with someone else's land, a trespass is committed. Trespass is a civil wrong, and you can be sued for doing it. The most common example of trespassing is when you go onto someone's land without their permission.
The corresponding Commonwealth offences do not require that a warning be given but provide for a defence of "lawful" or "reasonable excuse" (section 89(1) Crimes Act 1914 (Cth) and ss.11(1) and 12(1) Public Order (Protection of Persons and Property) Act 1971 (Cth) ). The penalty for both is a fine of up to $1000.
Trespass on certain types of premises is governed by different Acts; e.g. Regulation 35 of the Defence Force Regulations 1952 (Cth ) authorises the Minister to declare a place to be a prohibited area and creates offences of entering or remaining without permission. The maximum penalty is $2000 or imprisonment for six months, or both.