Last night's debate was the last before polling day - but it was also the biggest.

The TVNZ 1 debate saw Mike Hosking chair a feisty debate between National leader Bill English and opposition Labour leader Jacinda Ardern.

Political commentators said English came out on top, with Heather du Plessis-Allan saying: "It's the first time Ardern has looked rattled."

Read more: Bill English vs Jacinda Ardern leaders' debate: The verdicts are in

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Newly releases statistics show 643,000 Kiwis tuned into the debate in the 5+ age bracket, up from the first debate which had 602,900 viewers.

Those aged between 25-54 numbered 213,000, down from 259,500 viewers.

John Gillespie, TVNZ's Head of News and Current Affairs, put the record numbers down to what's shaping up to be a dramatic polling day on Saturday.

"The Election appears to be on a bit of a knife-edge and it showed in last night's intense debate," he said.

The debate came after a new 1 News Colmar Brunton poll that place the National Party rising six points to 46 per cent and Labour down seven points to 37 per cent.