New Zealanders have been stunned by the All Blacks' first ever home series loss to Ireland and are contemplating changes to their men's national rugby team.

Once were warriors; now they're just worried.

The All Blacks' slump has engaged New Zealanders in a national bout of introspection and exasperation, much centred on besieged coach Ian Foster.

Before last week, the All Blacks had never lost a home Test to Ireland, let alone a series.

Back to back losses in Dunedin and Wellington now have the All Blacks in an unfamiliar and uncomfortable position: their lowest ever position of No.4 in world rugby rankings.

New Zealand's form reversal has been whiplash-inducing.

Before COVID-19, they suffered five defeats to European sides in a decade, but under Foster, they've lost four times in eight months.

"None of us are used to that," former star All Black winger Sir John Kirwan told Newstalk ZB.

"It was a bit of a shock for everyone to see that happening ... there's a lot of negativity out there.

"The All Blacks have a lot of soul searching to do."

The series defeat - their first at home to anyone since 1994 - has prompted a vast array of emotions from rugby-loving Kiwis.

One lowered the nation's flag outside New Zealand Rugby's headquarters in Wellington, a short walk from the scene of Saturday's 32-22 loss, which followed the 23-12 defeat in the second Test.

Talkback callers have unleashed all manner of criticism: blaming complacency, Sam Cane's underwhelming leadership as captain, New Zealand Rugby, team culture, a private equity sell-off, the Barrett brothers and more.

Pressure mounts most of all on Foster, who boasts the lowest win percentage of any All Blacks coach since the mid-1990s.

Foster dead-batted questions on his future after Saturday's Test and didn't front for a scheduled media appearance on Sunday.

New Zealand Rugby has closed ranks, refusing media requests, issuing only a brief statement from chief executive Mark Robinson.

"Clearly the performance across the series for the All Blacks was not acceptable," he said.

"We all know there is a huge amount of work to do. Our focus now is to work with Ian and his team to understand thoroughly in advance of the Rugby Championship what is needed to improve performance and where to from here."

Sir John called that statement a mistake.

"New Zealand Rugby shouldn't have said we're going to review. They should have said 'we support him' or 'we don't'," he said.

"Saying we're going to do a review has created way more fuel for the fire."

Foster was appointed after the 2019 World Cup, elevated from his assistant position under the retiring Steve Hansen on a two-year deal.

After two southern hemisphere titles, he was handed a two-year extension last year to see him through to the 2023 global showpiece tournament.

In 2019, when the All Blacks lost their world title in a semi-final loss to England, Foster was given the job in a straight shoot-out with Super Rugby title machine Scott 'Razor' Robertson.

Foster was the company man, the continuation of business as usual, and a vote of confidence in Hansen's All Blacks game plan.

Robertson was the outsider, the change agent, the wild man known for breakdancing after championships.

At the time, Robertson had won three consecutive Super Rugby titles with the Crusaders. He now has six straight.

Many - particularly Cantabrians - would prefer him in the top job ahead of next year's World Cup.

They may receive their wish, especially if New Zealand under-achieve in South Africa next month for two Tests to begin the Rugby Championship.

"He wins (the Rugby Championship) and we see some signs of improvement then I think he'll survive," Sir John said.

"If he doesn't then I just don't know what will happen."