New Zealand's super-rich were found liable for an extra $77 million of tax in the last financial year.

The country's most well-off have paid hundreds of millions of dollars in extra tax to Inland Revenue since it set up its high-wealth individual unit in 2003.

Those who come under the scrutiny of this IRD division must have, or be in control of, more than $50 million.

According to IRD's investigation and advice manager Tracey Lloyd, the unit has identified 200 people who met the criteria.

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Of these 200 people, 93 declared their personal income in the 2013 financial year as less than $70,000 - the point at which one is required pay the top tax rate of 33 cents in the dollar.

IRD said income declarations for 2014 are not required to be filed until the end of March and therefore it does not hold details on them yet.

The 2013 proportion is slightly lower than seen previously and Lloyd pointed out it was common for income associated with these individuals to be declared in other entities such as trusts and companies.

Indeed, these 200 high-wealth individuals are in control of, or closely associated with, 6809 entities, according to IRD records.

IRD was unable to reveal the number of these taxpayers it may be investigating, as this could make it possible "to form inferences about particular individuals", given the small pool of people involved. Nor was IRD able to divulge the number of tax-planning devices these people employ.

While unable to comment on how much tax it believed these high-wealth individuals had underpaid, the IRD did say it had assessed another $77 million to members of this super-rich group in the year to June 30. This amount is over and above what these individuals had already paid in tax.

A reassessment of tax does not always mean the full amount will be paid and IRD said it often results in a reduction in net losses or tax credits available to use in later years. While IRD and high-wealth individuals were in disputes over $112 million of tax, these reassessments are not part of this.