UPDATE: 11:26 AM
The Turnbull government faces a possible constitutional crisis after Deputy Prime Minister Barnaby Joyce was told he could be a citizen of New Zealand.
Mr Joyce told parliament on Monday the New Zealand High Commission contacted him last Thursday with the "shocking" information.
"On the basis of preliminary advice from their department of internal affairs - which had received inquiries from the New Zealand Labour Party - they considered I may be a citizen by descent of New Zealand," Mr Joyce said.
Under section 44 of the Australian Constitution, anyone who holds dual citizenship is ineligible to sit in parliament.
Mr Joyce - whose eligibility will be referred to the High Court - won't be stepping aside from cabinet, unlike his Nationals colleague Matt Canavan who discovered his mother signed him up for Italian citizenship.
The Nationals leader told parliament he was born in Tamworth in 1967 to an Australian mother and was fifth generation Australian.
"My father was born in New Zealand and came to Australia in 1947 as a British subject. In fact we were all British subjects at that time," he said.
"The concept of New Zealand-Australian citizens was not created until 1948."Neither my parents nor I have ever applied to register me as a New Zealand citizen. The New Zealand government has no register recognising me as a New Zealand citizen."
The prime minister has asked that Mr Joyce remain deputy prime minister and continue his ministerial duties."
The government is satisfied that the court would not find Mr Joyce disqualified to sit in the House," Mr Turnbull wrote in a letter to Labor leader Bill Shorten, released on Monday.
The prime minister offered Mr Shorten "the opportunity to nominate any Labor members or senators whose circumstances may raise questions under section 44 of the constitution" so the parliament can also refer those matters to the High Court.
"It would be helpful if all relevant matters could be heard by the court at the same time."
The Australian people must have confidence in our political system and resolving any uncertainty is vital."
Including Mr Joyce, the High Court is now considering the futures of five MPs, with August 24 already set aside to hear cases involving Senator Canavan, former Greens Scott Ludlam and Larissa Waters and One Nation senator Malcolm Roberts.
According to the NZ government passport website: "If you were born overseas and at least 1 of your parents is a New Zealand citizen by birth or grant, you are an NZ citizen by descent. To get yourself an NZ passport, you need to register your citizenship.
"If Mr Joyce is found to be ineligible, the government - which holds a one-seat majority in the lower house - would be forced into a by-election
Labor frontbencher Anthony Albanese said the party had a "rigorous" process in place for would-be candidates and no one in the caucus had any adverse citizenship issues.
Deputy Prime Minister Barnaby Joyce has told parliament he may be a citizen of New Zealand.
The New Zealand High Commission contacted the Nationals leader on Thursday afternoon to advise he may be a citizen by descent.
Mr Joyce told SBS on Monday he was shocked to receive that information, adding he had been born in Australia and had always been an Australian.