OECD data shows the number of years people take to qualify for a full state pension.

New Zealand's got a reputation for being friendly to immigrants, but the Retirement Commissioner thinks it's being just a little too friendly when it comes to NZ Super.

Commissioner Diane Maxwell has copped abuse for proposals released on Wednesday to cut state pension entitlements, including lifting the age people get NZ Super to 67 by 2034.

But there's one suggestion she's not been criticised for: increasing the time immigrants must be resident before getting NZ Super from 10 years to 25 years.

SUPPLIED Retirement Commissioner Diane Maxwell says the pension age must rise in New Zealand.

What wasn't immediately clear was that Maxwell meant her policy to also cover New Zealanders living overseas.

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Maxwell, who has a statutory duty to advise Parliament every three years on retirement income policy, thinks people should have 25 years as an "ordinary resident" in New Zealand after the age of 20 before they qualify for NZ Super, though they would qualify for emergency benefits if they fell on hard times before that.

Work would need to be done on an implementation plan, Maxwell's office says, but the proposal, if MPs passed it into law, would likely apply immediately to new migrants to New Zealand, but be phased in for New Zealanders currently resident here, who may opt to head overseas to work, and those already living overseas.

The current ten-year eligibility rule dates back to 1972 when most migrants were British, and their UK state pensions could be deducted from NZ Super, with taxpayers here and in their old homeland sharing the costs of funding their super.

These days many migrants come from countries like China where there is no state pension to help pay for NZ Super, which pays a married couple, who both qualify, $34,916.96 a year before tax.

New Zealand First welcomed Maxwell's proposal, while decrying her suggestion to lift the age of eligibility to 67.

The party anticipated her migrant call by tabling a private members' bill in October in Parliament calling for the shift from 10 to 25 years.

In his bill, NZ First MP Denis O'Rourke says: "Globally, 10 years is an unusually short time for full entitlement to a universal, non-means tested pension at age 65. Considering average life expectancy, New Zealand Superannuation is paid for 20 years, which is up to $460,000.00 per person at current rates."

The OECD in its Pensions at a Glance survey notes: "Australia and New Zealand are the OECD countries with the lowest residential eligibility criteria, as full benefit is paid after residing in the country for only ten years."

But Maxwell's recommendations fall short of NZ First's when it comes to New Zealanders returning from Australia to retire.

There are an estimated 600,000 New Zealanders in Australia, where the retirement age will begin rising to age 70 in a series of steps starting next year.

Australia's compulsory super savings regime means they are amassing far larger nest eggs than people living here are using KiwiSaver.

Yet under current policy settings they are able to return to New Zealand at age 65 to retire, immediately qualify for NZ Super, and have to contribute nothing from their super nest eggs towards paying for it.

That's because New Zealand's social security treaty with Australia says years spent as an ordinary resident in Australia count as years spend in New Zealand for the purposes of NZ Super qualification.

O'Rourke says his bill would mean New Zealanders overseas, including in Australia, would only qualify for NZ Super when they had been actually resident here for 25 years over the age of 20, so returning New Zealanders would have to live off their savings until they qualified for NZ Super.

New Zealand faces a surge in pension costs, if the change isn't made.

"It's not just Australia," O'Rourke says. "It's other countries like the UK and Australia raising their retirement age. People will come back to New Zealand to get NZ Super at age 65. We need to pay attention to this."

Auckland University academics Claire Dale and Susan St John, in their study New Zealand Superannuation Policy and Overseas State Pensions, say: "With Australia increasing the state pension age from 65 to 67 between 2017 and 2023, and introducing a harsher income test...New Zealand may become an even more attractive place for Australians to retire."

The academics said the Ministry of Social Development, which administers NZ Super, told them there were "policy interventions that could minimise the risk of New Zealanders returning to New Zealand to access NZ Super while the Australian Age Pension age of entitlement is rising."

It's not clear what those policy interventions are, but unless New Zealand First gets its way, it may add to pressure to lift the age of eligibility of NZ Super to match Australia's.