Northcote has a new MP - the National Party's Dan Bidois.

Bidois won tonight's byelection by more than 1300 votes over Labour's Shanan Halbert.

National leader Simon Bridges said he was proud to welcome Bidois to what he described as an "energised" team of 56 in Parliament.

"Tonight Dan - you are the man."

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Bidois was going to be a champion for the area, Bridges said.

"The people of Northcote know they vote and they support the party that is for a stronger economy, that's for lower taxes, lower costs, that isn't going to go soft on law and order, that isnt going to go soft on welfare, that believes and back them every day we can."

Bridges, accompanied by his wife, Natalie, thanked deputy leader Paula Bennett for running the campaign.

Bidois said it was an overwhelming result. He had been a fighter all his life and he would be a fighter for Northcote, he said.

One of the first things he was looking forward to doing was voting against the regional fuel tax.

Bidois, a 35 year-old Foodstuffs executive, only moved into the electorate after he was selected but will now make it his permanent home.

Prime Minister Jacinda Ardern said Labour "had a lot to be proud of" from the result. It had slashed the majority in a National stronghold, she said.

"We have grown from a party which was polling 30 per cent in the seat to one that polls over 40."

"Shanan continued that trend here tonight."

Halbert, who increased his vote by 10 per cent on the general election, said he would run again in 2020, and sent a warning to Bidois.

"He has two years. We will be watching."

Most of his higher vote came at the expense of NZ First - who did not run a candidate - and the Greens. National's vote stayed relatively stable at around 51 per cent.

Green candidate Rebekah Yaung won 579 votes and the Act Party's Stephen Berry got 157 votes.

The seat was vacated by former National MP Jonathan Coleman, who resigned to take up a role with Acurity private hospital.

He won Northcote in last year's election with a majority of 6210, down from his majority of 9664 in 2014.

Turnout was down on the general election. Around 21,000 people voted, compared to 36,995 in September.

Voting closes

Voting has closed in the Northcote byelection and party volunteers were watching the results come in.

Figures released by the Electoral Commission today show that 11,464 of the 48,077 enrolled voters cast a vote in the two weeks of advance voting.

That is up a little on advance voting in the electorate at the September general election which, at 10,755, was just over 22 per cent of voters.

Advance voting in the Northcote byelection was higher than occurred in the Mt Albert by election last year and Mt Roskill's in 2016 but not as high as Northland's in 2015 when National lost the seat to New Zealand First leader Winston Peters.