National leader Christopher Luxon insists a potential coalition partner's policy is "madness" and will not happen, while lumping the left bloc's "nine new taxes" together as certainties.

National has consistently attacked Labour "and its mates" (the Greens, Te Pāti Māori and Opportunity), saying combined they would impose nine new taxes.

Labour has only committed to its own capital gains tax.

Meanwhile, New Zealand First - National's potential coalition partner if it wins the November 7 election - is campaigning on buying back the BNZ for about $20 billion.

Luxon told RNZ’s Morning Report programme on Monday "that's just not going to happen".

"It's absolute madness," he said.

Morning Report's John Campbell put it to Luxon that Labour leader Chris Hipkins could say the same for his potential coalition partners' policies.

Luxon replied that Hipkins would "have to do business" with the Greens, Te Pāti Māori and Opportunity.

"He can't find a pathway to get into government without those four radical parties and six leaders, that's going to be chaos.

"He is going to implement those nine new taxes."

Both National and Labour held their campaign launches in Auckland on Sunday.

Luxon unveiled a list of 10 promises, including economic growth, no new taxes, better infrastructure and tougher consequences for criminals.

He told the crowd National had delivered this term but "the job isn't done".

Campbell asked Luxon what more he wanted to achieve.

"We've really got to continue to drive really hard into economic growth," he said.

"We can see all the economists talking about our economy strengthening and growing faster than people had anticipated, which is all good, but you know, we want to just continue that plan."

At Labour's launch, Hipkins released a new policy, promising to write off 10% of eligible student loan balances.