Labour leader Jacinda Ardern and National leader Bill English went toe-to-toe in the second debate of the election campaign, this time a 90-minute long debate on Newshub at 8.30pm with the Newshub political editor as moderator.

The leaders traded blows on homelessness, housing, tax and economic policy in a more hostile debate than that hosted by TV 1 last week.

National's finance minister Steven Joyce set the theme early in the day by claiming Labour had an $11.6 billion hole in its fiscal plan.

Finance spokesman Grant Robertson was quick to counter, saying most of the amount Joyce claimed was a hole in its operating allowance had been accounted for in other lines of its budget. He described it as a "desperate, cynical stunt to create a diversion".

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However, English will be out to try to make the line that Labour can't be trusted with the economy stick tonight.

English is also likely to reprise his attacks on Labour's tax policy as it continues to refuse to rule out introducing taxes such as a capital gains tax in its first term.

A Newshub Reid Research poll on Sunday night showed National had slipped down slightly to 43.3 per cent, while Labour was up another six points to 39.4 per cent.

As English was at 30 per cent as preferred PM and Ardern was on 29.9 per cent.

Ardern said National's attempt to discredit Labour's economic plan was clearly a campaign ploy.

"Both parties are battling hard here, for good reason. It's on the line."

In the last debate on TV1 on Thursday night, neither Ardern nor English managed to land a killer blow of the size of John Key's slayer "show me the money" line at Phil Goff in 2011. Both will be trying for it tonight as polls show they are neck and neck.