The richest 10 per cent of New Zealanders are wealthier than the rest of the population combined, according to figures cited by Oxfam NZ.
The charity says the numbers illustrate a stark wealth gap in New Zealand, which is deeply worrying - and wants multinational corporate tax avoidance addressed.
However, the Government says its own analysis shows inequality has not worsened in the past decade, and the system already redistributes a significant amount of income.
Rachael Le Mesurier, Oxfam NZ's executive director, disagreed, and said we were becoming more divided, "with an elite who are seeing their bank balances go up, while hundreds of thousands of New Zealanders struggle to make ends meet".
Oxfam says data from the 2013 Credit Suisse Global Wealth Databook also shows that the top 1 per cent of Kiwis hold more wealth (25.1 per cent) than the bottom 70 per cent.
Asked to comment on Oxfam's figures yesterday, a spokesman for Finance Minister Bill English said its own reporting showed inequality was not worsening.
"The most comprehensive report on inequality published annually by [the Ministry for Social Development] shows inequality has not got any worse in New Zealand in the past decade."
Billions of dollars a year went to support low-income New Zealanders, the spokesman said, and the tax and income support systems provide significant income redistribution.
This year's Budget provided further measures such as free doctors' visits for children and extended paid parental leave.
"The best contribution the Government can make to support lower income families is to support a growing economy that provides more jobs and higher incomes."
At the invitation of Australia, New Zealand will join a G20 meeting in Melbourne this weekend.
Ms Le Mesurier said the group of nations last year endorsed a plan to address multinational tax dodging, and questioned whether New Zealand had taken enough action on the issue.
In response, Revenue Minister Todd McClay said New Zealand was in a comparatively strong position on such issues compared to many countries.