If you wilfully or negligently destroy or damage works or property, you could be committing an offence. This is stated in a part of the Local Government Act 1974 called 'Wilful or negligent destruction of or damage to works or property'. However, this part of the law has been repealed, which means it is no longer in effect, and was repealed on 1 July 2003 by section 266 of the Local Government Act 2002, which can be found at https://legislation.govt.nz/act/public/1986/0120/latest/link.aspx?id=DLM174092.