The gap between women's and men's median incomes has widened to the biggest gap since 2008.

Women's median pay rose by only 50c in the past year, from $20.73 an hour in June last year to $21.23 an hour this year, while the male median rose by $1.07 from $23 to $24.07 an hour.

The gap of 11.8 per cent is the widest in Statistics NZ's annual income survey since June 2008, when it was 12.5 per cent.

The gap narrowed dramatically to just 9.3 per cent at the worst point in the recent recession in 2012, when ironically more low-paid women losing their jobs raised the median income of those women still in paid work.

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But as more low-paid women have been pulled back into paid work as the economy has recovered, the gender pay gap has widened again.

Maori and Pacific median pay rates for men, and Maori pay rates for women, have also dropped as a proportion of male European pay rates for the same reason, as the recovery generates more low-paid jobs.

But Pacific women have bucked the trend, boosting their median pay rates as a proportion of male Europeans in both the past two years.

Green Party women's spokeswoman Jan Logie blamed the widening gap on "National's hands-off approach to gender equality".

"Women are literally paying the price for National's do-nothing approach," she said.

Minister for Women Louise Upston said she was also disappointed by the widening gap and called for action by workers, employers, careers advisers and business leaders.

"Women should be encouraged into fields where they have been traditionally under-represented," she said. "Many of these areas, such as technology, construction and trades are experiencing high growth and high wages."

Over the longer term, separate figures from the quarterly employment survey show that the gender pay gap closed sharply after the Equal Pay Act of 1975, and again in the late 1980s and more slowly from 1997 to 2009.

The later two periods of gains coincided with Labour governments when unions were relatively strong, reflected most notably in a big 20 per cent pay rise for public sector nurses in 2005.

But the improvements stalled when unions were weakened first by the Employment Contracts Act of 1991 and again by changes such as the 90-day trial period under the current John Key-led Government which took office in 2008.

Looking over the past decade as a whole, the income survey still shows a long-term narrowing of the gender pay gap from 14.3 per cent in 2005 to 11.8 per cent today.

Women in all ethnic groups now earn significantly more than a decade ago relative to the highest-paid group, male Europeans. European women earn 13.3 per cent less, Asian women 21.2 per cent less, Maori women 25.1 per cent less and Pacific women 27.4 per cent less, than European men.

But the ethnic pay gap has actually widened for Maori men, who now earn 20.9 per cent less than European men, a wider gap than a 17.2 per cent gap in 2005.

There has been little change for Asian and Pacific men, who still earn 13.3 per cent less and 23.1 per cent less respectively than European men.