Australia's Liberal Party federal director Brian Loughnane has become involved in the New Zealand election, encouraging Kiwis in Australia to help re-elect John Key's National government.

In an unusual move, Mr Loughnane has launched an online campaign to encourage Australians with NZ friends living and working in Australia to vote National.

"Without the party votes of National supporters living overseas there is a real risk that Labour will cobble together a coalition government with the Greens and other minor parties," Mr Loughnane writes.

"Under the leadership of John Key and National, New Zealand is moving in the right direction."

Kiwis in Australia have until this Friday to vote.

Australian National University political scholar Professor John Wanna said it was a "strange" intervention in the NZ political process.

"The normal protocol is people don't get involved in each others' politics and policies but that's been breaking down," he told AAP.

"It's a historical convention to let other countries sort their own politics out."

However he said conservative parties were increasingly seeing themselves as part of an international network.

Prof Wanna said NZ National feared the possibility of having to form a coalition with minor parties after the election and was trying to maximise the single party vote.

More than 640,000 New Zealand citizens are in Australia, representing a large proportion of the NZ electorate.