Who prosecutes election-related criminal offences?

Criminal Procedure Act 2011

http://www.legislation.govt.nz/act/public/2011/0081/latest/096be8ed80fe3d74.pdf

s 185 (1): The Solicitor-General is responsible for maintaining general oversight of the conduct of public prosecutions.

s 187: (1)  The Solicitor-General must assume responsibility for and conduct every Crown prosecution from the time or stage in the proceedings prescribed in regulations. (2) The Solicitor-General's duty under subsection (1) may be performed by any Crown prosecutor.  

s 188: A Crown prosecutor who conducts a Crown prosecution under section 187 must conduct that prosecution in accordance with any directions given by the Solicitor-General (either generally or in the particular case).