The Opposition is accusing Jacinda Ardern of creating "policy on the hoof" after her promise of no new regional fuel taxes while she is Prime Minister.

But Ardern said the only reason she made the promise today was "for the sake of clarity" after National Leader Simon Bridges had been spreading "utterly, incorrect and false" information.

Speaking in the general debate this afternoon in the House, Bridges said Ardern had made "policy on the hoof".

Just an hour beforehand, Ardern had made the surprise announcement there would be "no other regional fuel taxes while I am Prime Minister."

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Under the regional fuel tax legislation, other councils are able to bid for a regional fuel tax from 2021 onwards.

But Ardern chose to make it clear that no other region would be getting the tax despite what the legislation said.

Associate Transport Minister Shane Jones said he learned of Ardern's decision in the House today.

"When you're in charge, take charge," he said, when asked about Ardern's announcement, adding he "thoroughly supported the Prime Minister's decision".

"It's highly likely there had been a host of discussions, but I'm being straight up – my focus is slightly elsewhere and I filled in for Mr Twyford."

Phil Twyford is the Transport Minister and was away from the House during question time today. Jones, as the Associate Minister, filled in to answer oral questions.

National's Transport Spokesman Paul Goldsmith said the fact the first Jones had heard about the policy was in the House today was "pretty extraordinary".

"The Government has been saying all along that they have brought in a regional fuel tax in Auckland and they have legislated for it to be able to go to other regions, such as Wellington, in 2021."

He said today's comments were "total policy on the hoof".

Despite this, he said National absolutely supports Ardern's call.

"But the point is this is a Government that is making it up on the fly."

Hamilton City Council was interested in a regional fuel tax, and councillor Dave Macpherson said Ardern's comments were surprising - and a kick in the guts.

"We're facing massive growth increases, particularly in the Hamilton-Auckland corridor, and we're putting in $230 million over the next 10 years on top of our normal transport budget to fund what we can. We're maxed out," said Macpherson, who also chairs the council's growth and infrastructure committee.

He said a 10c regional fuel tax would have allowed motorists to ease the financial pain.

"It wasn't going to break the bank. It made sense, we thought. We put up rates in July by 9.7 per cent. We think we're doing our bit, and more. The Government is going to have to stump up."

Tauranga Mayor Greg Brownless, who previously expressed an interest in the tax, welcomed Ardern's ban – as long as the Government built the roads the council needed in a timely fashion.

"Fuel taxes are always controversial. Our interest in them was if they were going to be the only method of funding roads, then we didn't want to miss out," Brownless said.

"[Ardern's ban] does also imply there is sufficient money in the existing budget for the roading projects we are desperately in need of."

If there wasn't sufficient money, "then that's a problem".

"They've got to find the money. The current state of the roads here is jeopardising access to our port. They need to be funded sooner rather than later."

This morning, Bridges told The AM Show Wellington City Council confirmed it was in early discussions about a fuel tax.

Wellington City Council spokesman Richard MacLean told Newshub the council had been in early discussions with the Government.

Ardern denied this and told reporters Bridges had spread "utterly, incorrect, false" information about a Wellington fuel tax.

In a tweet, Wellington City Council Mayor Justin Lester said: "Wellington has zero interest in implementing a fuel tax across the region. We are not discussing it with the Government."

- Additional reporting from Derek Cheng