Jacinda Ardern denies Labour was dirt-digging on Australia's Deputy PM Barnaby Joyce

Labour leader Jacinda Ardern says she has reprimanded MP Chris Hipkins' for raising questions on citizenship after talking to the Australian Labor Party but denied he was part of a dirt-digging exercise on Australia's Deputy PM Barnaby Joyce.

Joyce this week was told by the New Zealand government that he had New Zealand citizenship by descent - MPs in Australia are barred from having dual citizenship and the rule has already seen two Green MPs leave Parliament.

Speaking in Parliament, Joyce said the New Zealand officials were prompted to look into it by queries from the NZ Labour Party, although Internal Affairs Minister Peter Dunne has since confirmed officials were first prompted by an Australian journalist rather than Hipkins.

Hipkins had put in two Parliamentary written questions to Internal Affairs Minister Peter Dunne about the legal status of an Australian born to a New Zealand parent on August 9, just after an Australian journalist asked about Joyce's situation.

Ardern denied Labour had been trying to help their Australian counterparts on a dirt digging exercise, saying Hipkins had not known questions asked of him by an "acquaintance" in the Australian Labor Party related to Joyce. Hipkins had not known the law so had put in formal written questions to Dunne.

She admitted Hipkins had an inkling of what the general issue might be, given two Green MPs had had to stand down because they were found to have dual citizenship.

She said it was now clear the inquiries were prompted by the Australian journalist rather than Hipkins.

"However, Chris himself has acknowledged that had he known what those questions would be used for, he wouldn't have asked them. And I've certainly relayed to him that it's my expectation that we focus on our own election rather than matters that are of no concern to us.

He didn't know who was involved but I've made it clear to him that regardless of those circumstances this is not an issue that we should have been involved in."

Joyce has asked the High Court to look at the case, saying he had not been aware he was a New Zealand citizen - it was automatic because his father was New Zealander.