Wow, Events are still changing faster than regulations.
If you are an Australian citizen or a permanent resident you cannot leave Australia due to COVID-19 restrictions unless you have an exemption.
I just read through these.
New Zealand safe travel zone | COVID-19 and the border
Exemptions include picking up a sick child, national interest, education of more than 3 months etc. There is a clause about work contracts that could be used for some for travel to NZ.
It appears that the rules have not been amended for NZ travel. If you have to apply for an exemption there seems to be no "quick holiday to see relatives in covid free area" exemption clause.
It is also unclear about what happens if you are a Aus citizen
living in NZ. If you travel back to Aus for a visit, it looks like you would have to apply for an exemption to leave and return to NZ.