The number of super-rich earners on the New Zealand taxman's radar has skyrocketed in the past five years with 350 people now worth more than $50 million — some of whom are in a fight over more than $85 million in disputed tax.

The group - labelled High Wealth Individuals (HWI) by Inland Revenue - has soared 75 per cent since 2013, while the country's poorest residents continue to struggle.

The numbers have been described by commentators as extraordinary.

In the 2018 tax year, Inland Revenue was attempting to claw back $85.8m in disputed tax from some of those individuals and their associates, companies, partnerships, trusts and related individuals.

That figure could fund Prime Minister Jacinda Ardern's $470,000 salary for the next 180 years.

Wealth and New Zealand author Max Rashbrooke told Mike Hosking there's a clear acceleration at the top end.

"There's some basic questions about fairness. You've got people in middle New Zealand working hard who don't see their wealth increasing, in fact they are probably treading water, they are probably looking at that and thinking is that a fair distribution."