Prime Minister Jacinda Ardern throws doubt on Vernon Tava's Sustainable NZ

Jacinda Ardern has hit out at the newest political party Sustainable New Zealand, saying the Government is already catering to the environmental needs it's offering. 

"I do believe that environmental matters are a huge focus for this Government and I don't see that there's necessarily a space that [Sustainable NZ] need to fill," the Prime Minister said Monday.

Sustainable NZ, launched on Sunday by former Green Party member Vernon Tava, promises to boost environmental conversation funding by $1 billion over four years.

Tava has fashioned the party as focusing on the environment and "making money while we're doing it", and he's willing to work with either Labour or National.

But Labour leader Ardern questioned the need for Tava's party in the current political space, asking reporters at her post-Cabinet press conference: "What is the political issue that they are trying to solve?"

Ardern said the current Labour-Green-New Zealand First Government is already doing plenty for the environment, pointing to the Zero Carbon Bill that passed its final reading last week.

She also reflected on the $181.6 million funding boost over four years given to the Department of Conservation in Budget 2018 - the largest bump in conservation funding since 2002.

"If they claim that they are operating in an environmental space... I'd say that it's being very well catered for by this Government," Ardern said.

She also highlighted Green MP Eugenie Sage's work as Conservation Minister, pointing to waste reduction initiatives, including a proposal to hold companies responsible for where their products end up.

Tava, who quit the Greens after failing to win the leadership contest in 2015, has criticised the party before saying it's become "too socialist".

On Monday, he told The AM Show his new party would embrace economic policies the Greens won't.

"We can't ban and tax and protest our way to prosperity. Our vision is not only can we protect and regenerate the environment, we can actually make money while we're doing it."

Tava said the idea that economic growth and capitalism "is somehow the enemy of the environment is incorrect - that's a core assumption that we're really challenging".

He said if Sustainable NZ was in a position to choose the next government, they'd start by talking to the party that received the most votes.

National was ahead of Labour by two seats on 56 in Newshub's poll last month, but it would need 61 seats to win. Labour was on 54, and with the Green's eight seats, it would have enough to form a government without NZ First.

Ardern took a massive drop in the preferred Prime Minister ranking, down 10.6 percent to 38.4 percent. But she was still way ahead of National leader Simon Bridges on 6.7 percent.