Australia's Deputy Prime Minister Barnaby Joyce has spoken of the "shell shock" of learning he is a Kiwi - and condemned a Labour MP for "playing" with another country's government.

Joyce's surprise New Zealand citizenship has sparked an extraordinary row between the Australian Government and New Zealand Labour Party.

In an interview with Sky News Australia he said he was still in shock at the news he is a citizen by descent, as his father was born in New Zealand.

Read a timeline of events by clicking here.

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"The most stunned people in this one were my parents - they kept on saying to me, 'No, you're wrong'... it is what it is. And now we have to manage it," Joyce said.

"It's fate, isn't it. When my father came over to Australia he was a British subject resident in New Zealand... there was no citizenship laws. They didn't exist until 1948, and Australia's weren't enacted until 1949."

Joyce told Sky News the actions of Labour MP Chris Hipkins in the case made it "sound awfully like the Labour Party talking to the Labor Party".

"And the problem with that is it's our nation's government that they are playing with. To be quite frank, the leader of the Labour Party [Jacinda Ardern], she sort of slapped the fella down in New Zealand, then the Prime Minister of New Zealand sort of doubled-up on it and slapped him down as well.

"You just got to have an absolute clean slate on that one, you've got to - don't even look like you are interfering in another country's internal politics. It's not a case of whether you have or haven't. Don't even look like it."

Australia's Constitution requires MPs to only hold Australian citizenship - and the Australian Government of the Liberals and the Nationals has a majority of just one seat.

Queries from Australian media reached New Zealand Internal Affairs in August.

Two days later Labour MP Chris Hipkins lodged Parliamentary written questions with Internal Affairs Minister Peter Dunne that related to the issue of New Zealand citizenship by descent.

He did so after a conversation with Australian Labor Party staffer Marcus Ganley, who is the chief of staff for Australian Senator Penny Wong.

Ganley was an adviser to former PM Helen Clark and former Finance Minister Cullen during the Labour Government until 2008. He then advised Phil Goff as Opposition leader.

Hipkins has denied knowing there were questions about Joyce's citizenship, saying he asked the questions of Dunne to clear up the law.

However, his actions have led to Australian Foreign Minister Julie Bishop making the extraordinary statement that she would find it hard to trust a New Zealand Government led by Labour.

Those comments have in turn been criticised by many political commentators in Australia as an intrusion into New Zealand's election campaign.

Bishop has since pulled back on criticising NZ Labour, but has continued to claim the Australian Labor Party was trying to use NZ Labour to undermine the Government.

Speaking in Wellington today, Prime Minister Bill English said he was informed last Thursday it was likely Joyce was a citizen.

"The determination was made that the High Commissioner should convey that to him directly, rather than through answers to Parliamentary questions or the media.

"It was a significant mis-judgement by senior Labour people in New Zealand to get involved in it."