Jacinda Ardern gives her assessment of the second leaders' debate

Labour party leader Jacinda Ardern has claimed National's allegation the party's fiscal policy had an $11.7 billion hole was "a deliberate attempt to mislead the public".

Ardern gave her assessment of the second major party leaders' debate and what it meant for the general election on NZ Herald Focus this morning.

"I just think it was mischief making," she told NZ Herald Focus' Tristram Clayton of Steven Joyce's claim yesterday.

"What they've claimed is that we haven't inflation adjusted or built in population growth for health and education. Clearly we have. We've built that over time, it's in our budget. All I can say is that they were simply wrong and trying to raise questions in voters' minds that we simply shouldn't have."

She said Bill English changed tack during the debate last night claiming they had not left room for pay increases. She said the numbers used for that were taken from National's pre-election fiscal update so if the numbers were wrong it was because the Government hadn't factored it in.

Ardern also said she was pleased to see English promise last night to cut child poverty by 100,000 families in the next two to three years and said she believed Labour could do the same.

English got in the surprise pledge under questioning from moderator Patrick Gower.

That came after he launched a strong defence of National's record on child poverty, pointing to measures such as increasing the benefit rate and its Families Incomes package in this year's Budget.

Ardern called for a legislated target to reduce child poverty, saying her entire reason for being in politics was to eliminate child poverty.

"I don't doubt that Bill English is concerned by kids living in poverty. But what I want to see is the actions over the last nine years to prove that there's enough commitment there to make a change. Over the last nine years we have seen basically 10-15,000 kids out of poverty. That's not enough, we should be much more ambitious," she said.

"What I think he was meaning was reducing 100,000 against the number of kids living on a median income of 50 per cent or less. If that's what his target is I believe we can match that."

She said Labour had its own bill on child poverty which would see measures and targets in law so there would be no future debate on how widespread the problem was.

Ardern said she was also pleased National had recently acknowledged and taken steps to address paid parental leave, the methamphetamine problem, child poverty and homelessness but said it was too late.

"These have already persisted for nine years. Yes I'm pleased that they've now got a focus. I would have liked it a lot earlier."

During last night's debate, Ardern threatened retaliation on Australia if it went ahead with plans to make New Zealanders pay more for tertiary education.

This morning she said she stood by her comment on that and her commitment not to raise the age of superannuation while she was leader.

Immigration was another area of difference raised in last night's debate and Ardern defended Labour's plan to cut immigration by 20,000-30,000 a year.

Gower also tackled the leaders on housing policies, and English defended his record by saying Government action had led to a flattening of prices as supply started to kick up and loan-to-value ratios took effect.

Ardern responded that Labour did not want to see people lose the value in their homes, but it should not be as hard as it was for first-home buyers to get into the market.

It was the second time the two leaders had met and both were a lot more fired up and willing to confront each other.