New Zealand First leader Winston Peters refuses to say whether he still supports the prime minister in light of a recent attempt within National to overthrow him.

Given repeated opportunities to declare confidence in Christopher Luxon on Tuesday, Peters instead referred the question back to the National Party.

A spokesperson for Peters later clarified to RNZ that New Zealand First continued its steadfast support of the coalition.

The exchange came after a Herald Now interview on Tuesday, in which Peters expressed doubt at claims the recent leadership challenge was a "one-man coup".

"I've been in politics for a long time, but for the first time, I saw a one-man coup... if you can believe that," Peters said, laughing.

Heading into the debating chamber later that day, Peters said his remark had been made "more in jest than in fact".

"Look, that's yesterday," he said. "That's last week, that's another political party.

"I lead a giant, dynamic movement called New Zealand First on the rise. Talk to me about our future."

Asked whether he maintained confidence in the prime minister given last week's events, Peters paused and then replied: "I don't understand your question."

Given another opportunity, Peters said such questions should instead be put to the National Party.

"No, no, I'm not a member. I'm not a member.

"I'm the only guy the National Party ever expelled, right, and all these years, they've been regretting it, so go and ask them."

Reminded that he was a minister in Luxon's cabinet, Peters walked away from reporters.

In total, Peters was asked five times whether he had confidence in Luxon.

Posed the same question, New Zealand First minister Shane Jones directed reporters to ask Peters instead.

"Only one person talks for the New Zealand First Party on matters of coalition management and that is my leader."

Peters denies breaching Cabinet collective responsibility on harbour crossing

During the earlier interview on Herald Now, Peters also criticised the government's announcement of a new study into a second Auckland harbour crossing, calling it a "gross, shocking waste of money".

Peters said New Zealand First would put the harbour crossing decision out to tender immediately.

The comments prompted bemusement from Luxon on Tuesday morning, who said all three New Zealand First ministers "signed up for this decision" in cabinet.

Speaking later at Parliament, Peters clarified that New Zealand First had supported the appointment of a senior expert, but also thought better options were available.

He said he had not breached cabinet collective responsibility.

"I just pointed out that $100 million's been blown, with nothing to show for it. Here we go again.

"We've got a special control officer now, which we do support, to ensure we don't blow another $100 million. Got that?

"What I'm really saying is, why don't we do what we're doing in Marsden Point? Put the information out there, so people can tender and save all this cost."

ACT leader David Seymour said voters could judge for themselves whether Peters had breached cabinet collective responsibility through his comments.

"We've all been on teams. Most Kiwis have played soccer, rugby or netball, and you generally want people on your team that are on your team every week."

Seymour pointed out that Peters had not invoked the coalition's 'agree to disagree' provision.

"I don't discuss what happens in cabinet, but I clearly remember Winston being there for the discussion and participating in it."