Winston Peters recorded a landslide victory over Mark Osborne to claim the Northland seat from the hands of National.

Northland has a new MP - NZ First leader Winston Peters.

The political veteran romped home in the National stronghold in a by-election triggered only six months after Northlanders voted for an MP at the general election.

His main rival, National candidate Mark Osborne admitted it had been a "tough day" when he arrived at the campaign headquarters, more than 4000 votes behind Peters.

Jackson Meecham National candidate Mark Osborne concedes by phone to NZ First leader Winston Peters.

READ MORE: * The results as they came in

* Opinion: A wake-up call for National

* A 'tough night' for Mark Osborne

Peter Meecham/Fairfax NZ A National Party supporter reacts to the results showing Winston Peters' lead.

With 100 per cent of the votes counted, Peters secured a 4012 vote majority with a total tally of 15,359.

Osborne pulled in 11,347 and in a distant third was Labour's Willow-Jean Prime on 1315.

A cheer erupted at NZ First headquarters in Russel when the win was confirmed.

Getty Images, Fairfax NZ National Party candidate Mark Osborne, New Zealand First leader and new Northland MP Winston Peters.

Peters said it had been a long hard campaign.

"It just shows you that you should never ever think that something's not possible if you've done the preparation and got the commitment.

"I saw all the ridicule at the start and the jeering and laughter but we are committed to the North and we always thought we could win this campaign."

Asked if he would move to Northland now he was its MP, Peters ducked the question.

"I've been here so much I could have qualified to vote here today."

He said the message to National was "as clear as daylight".

"We've had a gutsful of being ignored, we've had enough of neglect, we want our fair share of the country's resources. We're the top half of export provinces in this country and look where we are economically We are wanting to see a fair apportionment of the wealth of this country, to the wealth creators of this country."

Peters said Osborne had called him "very generously" to concede and he had told him not to take the loss to heart.

"I said he was in the most impossible position trying to make up decades of neglect and it wasn't his fault and I wanted his wife and family to know that."

The resounding win is likely to send shockwaves through National - a traditionally safe National seat that it would been expected to comfortably hold on to.

Osborne made the call to Peters to concede before 9pm.

He'd arrived at the National Party camp about 8.30pm and was hugged by supporters and greeted with applause.

It had been "a tough night", he said.

Speaking to supporters, Mark Osborne said he had called Winston Peters to concede.

"I passed on my congratulations to him."

Osborne said he was proud of his campaign team.

"It's brought the best out of me."

It was "a difficult speech to make," Osborne said.

"I'm sorry it's not the result we all wanted."

Osborne said he had no regrets.

"I'm inspired more than ever to make a difference for Northland. We didn't come out on the right side of the ledger today but it hasn't stopped me wanting a better future for Northland.

"It was probably a bit of a perfect storm. It was a by-election that sort of came out of left field. Secondly you've got someone like Winston Peters who's got tremendous name recognition, and the third factor was that Labour threw Willow-Jean under Winston's bus."

Osborne said he told Peters "congratulations and well done".

"We'll be making sure he delivers for Northland over the next two and a half years.

"He said he knew it was pretty tough on me. I thought it was important to call him and acknowledge he'd won and wish him the best."

Osborne said he didn't have a "Plan B" post election.

"The reality is I've taken leave of absence from my job as asset manager for the Far North District Council. So I'll consider what I do over the next couple of days."

National cabinet minister Steven Joyce conceded Peters had campaigned well.

"He got the result he was looking for. It's tough for us but he deserves it."

The result may have reflected frustration among Northland voters, he said.

"It's an aspirational region and they may have felt they were not getting far enough ahead."