Greens cagey on Jacinda Ardern as Deputy PM

New Labour deputy leader Jacinda Ardern says being Deputy Prime Minister if the party wins the election isn't a "make or break" for her.

The Mt Albert MP has risen through the ranks, elected unopposed and unanimously by Labour's caucus to take over from long-time MP Annette King.

But the question of what a coalition government might look like with the Green Party after September 23 could put a strain on the parties' happy marriage.

Greens co-leader James Shaw refused to say if he would support a government with Ms Ardern sitting in the Deputy Prime Minister's chair.

When asked by Newshub if he would work with Ms Ardern as the government's second-in-command, Mr Shaw replied: "I'd be delighted to serve in a government with Jacinda Ardern."

But he repeatedly refused to say he would support Ms Ardern as Deputy Prime Minister, reiterating it would depend on the numbers on election night.

"You can get into all this game stuff of who gets what jobs but in the end, what matters is the results."

Mr Shaw says Ms Ardern's appointment doesn't mean he or fellow co-leader Metiria Turei will be shunted from the Deputy Prime Minister role, should they form a government with Labour.

"What it means is she's the deputy leader of the Labour Party," Mr Shaw says.

He denied feeling worried or threatened at all by her appointment.

"This is the thing about the coalition negotiations, they happen after the election once you know what the numbers are.

"Would we like to be able to occupy that role? Yes, but that depends on whether we're able to have enough MPs in the House to justify that position."

Ms Ardern said she was nearby when Mr Shaw was being grilled over the deputy prime ministership; she called him a good friend.

"[Being Deputy Prime Minister] hadn't even crossed my mind. It's not something I'm dwelling on or that feels particularly important to me," she told The AM Show on Wednesday.

"If we're in government, that's the main thing for me. That's my focus. The rest we deal with in the aftermath, in the wash up - what a happy problem to have.

"[Deputy Prime Minister's] not something that for me is make or break, for me it's getting into that position."

Regardless of who wants it, the Deputy Prime Minister role is likely to be demanded by New Zealand First leader Winston Peters if he's in the position of kingmaker.