Labour has smashed National's hold on provincial New Zealand, looking set to capture up to 18 formerly National seats based on early voting.

With just over half of the vote counted, Labour has grabbed the National seats of Whangārei, Northcote, Upper Harbour, Takanini, Hamilton East, Hamilton West, East Coast, Tukituki, New Plymouth, Whanganui, Rangitikei, Ōtaki, Wairarapa, Hutt South, Nelson, Ilam, Rangitata and Invercargill.

That means high-profiles National MPs such as deputy leader Gerry Brownlee (Ilam) Nick Smith (Nelson) and Chris Bishop (Hutt South) face losing their seats.

One or two of those may go back to National in the final tally, but Labour has swept up several seats that no one had ever expected the party to win.

Also, Green candidate Chloe Swarbrick is leading a three-way race in the former National seat of Auckland Central.

Labour has lost only one seat - the Māori seat of Waiariki, where Māori Party candidate Rawiri Waititi leads Labour's Tamati Coffey by the narrowest of margins, just 36 votes, with two-thirds of the vote counted.

Almost three-quarters of New Zealand's 65 general and seven Māori electorates were considered safe for the incumbents.

In 2017 National won the vast majority of the general seats - 41 out of what were then 71. This year it still leads in only 23.

Labour won only the seven Māori seats plus 22 general electorates - all except three of them in the traditional four main centres of Auckland, Wellington, Christchurch and Dunedin. The three exceptions were Napier, Palmerston North and West Coast-Tasman.

This year it is leading in 47 seats.

The only other party that won a seat was Act in Epsom, thanks to a longstanding sweetheart deal with National designed to make sure that Act votes were not wasted in years when the party fell below the 5 per cent threshold for list seats.

This year, the national polls suggested that Labour was within striking distance of National in 11 general seats: Northcote, Auckland Central, Maungakiekie, Takanini, Hamilton East, East Coast, Tukituki, Whanganui, Wairarapa, Hutt South and Nelson.

However, boundary changes and other local factors gave National a chance of recapturing five Labour seats: New Lynn, Te Atatū, Ōhāriu, Banks Peninsula and Taieri.

Labour was also at risk of losing three of its Māori seats to the Māori Party: Tāmaki Makaurau, Te Tai Hauāuru and Waiariki.

It was more of a long shot, but National also risked losing the seat of Northland to New Zealand First, whose leader Winston Peters held the seat from 2015 to 2017.

Both the Māori Party and NZ First are polling below the 5 per cent threshold nationally, so their only hope of getting into the next Parliament is by winning an electorate.

Labour's potential gains

Hutt South

National's most marginal seat in 2017 was Hutt South, won by National's Chris Bishop by just 1530 votes after Labour held the seat and its predecessors for 88 years.

Bishop has been a National star in the past three years, rising to seventh place in Judith Collins' current shadow cabinet with the portfolios of infrastructure, transport and Shadow Leader of the House.

Labour's 2017 candidate Ginny Anderson became a list MP anyway and is standing again in Hutt South and is leading Bishop by 574 votes.

Auckland Central

Former National Education Minister Nikki Kaye famously beat Jacinda Ardern twice in Auckland Central, in 2011 and 2014, and just held on in 2017 with a margin of 1581 over Labour's Helen White in 2017.

This time Kaye resigned just weeks before the election and National had to reschedule its candidate selection after party members complained about the way a shortlist was put together.

National candidate Emma Mellow, an ANZ Bank communications manager, was finally selected on August 10.

White is standing again for Labour and was ahead in pre-election polls, but has also had to battle against a Green Party campaign to elect Chloe Swarbrick in the seat as insurance in case the Greens fall below the 5 per cent threshold nationally.

White wrote on October 8 that Labour wanted to regain the seat which it held from 1919 to 2008 except for one term when it was won by Alliance MP Sandra Lee in 1993.

But with 76 per cent of the votes counted, Swarbrick is ahead with 8072 votes to 7598 for White.

Whanganui

Whanganui, National's third-most-marginal seat, has swung with the national trends throughout most of its history, but its default setting used to be Labour - Labour won it in 21 out of 23 elections from 1919 to 2002.

Local police officer Chester Borrows finally won it for National in 2005 and kept it until he retired at the last election when it was held for National by local lawyer Harete Hipango.

Labour's 2017 candidate Steph Lewis, also a local lawyer, is standing again this year and stands a good chance of riding the nationwide Labour tide to boost Labour's thin holdings in the provinces.

With 65 per cent of the vote counted, Lewis is miles ahead with 16,704 votes to Hipango's 10,051.

Maungakiekie

The Auckland seat of Maungakiekie (One Tree Hill) is another seat that was held by Labour through most of its history, as the former Ōnehunga seat, from 1938 until 2008 when National's Sam Lotu-Iiga won it.

Its current National MP, former Auckland councillor Denise Lee, blotted her copybook two weeks ago when she sent an email to all National MPs complaining that her leader, Collins, announced a review of Auckland Council without consulting Lee as the party's spokesperson on Auckland Council issues.

Lee's majority last time was 2157 votes, National's fourth-lowest. Boundary changes have made it safer for National this time, lopping off Panmure and adding in Royal Oak. Still, Ardern visited the seat this week to support Labour candidate and list MP Priyanca Radhakrishnan.

Lee remains ahead by 280 votes with half the vote counted.

Tukituki

Tukituki (formerly Hastings) was a typical bellwether provincial seat which went with the Government in most postwar elections until 2005 when National won the seat three years before John Key led the party to victory nationally.

National has held it ever since, but current MP Lawrence Yule's majority of 2813 in 2017 was still slim enough to make it vulnerable in a big Labour year.

Labour's Anna Lorck is having her third crack at the seat this year.

With 29 per cent of the vote counted, Lorck is ahead with 12,496 votes to 11,098 for Yule.

Wairarapa

Wairarapa has swung with the Government in most elections since 1935, but like most provincial seats it has been solidly National since 2005 - by a margin of 2872 in 2017.

Its current MP Alastair Scott is stepping down this year, and his National replacement Mike Butterick faces a tough challenge from well-known Labour list MP Kieran McAnulty.

With 68 per cent of the vote counted, McAnulty has a massive margin of 5257 votes over Butterick.

Nelson

Nelson's National MP Nick Smith is officially our "Father of the House" - the MP with the longest continuous service in Parliament as MP for Tasman from 1990-96 and Nelson since 1996.

Last time he held on thanks to a three-way split. The Greens, which have always done well in Nelson and targeted the seat in 2017, won 23.7 per cent of the vote for their candidate Matt Lawrey, while Labour's Rachel Boyack won 30.3 per cent.

Together they won more than Smith's 40.7 per cent, but the split cost the centre-left victory.

This year's Green candidate Dr Aaron Stallard says his priority is the party vote, leaving the centre-left field for the electorate vote clear for Boyack, who is again standing for Labour.

With 81 per cent of the votes counted, Boyack has a solid lead of 3551 votes over Smith.

East Coast

On the face of it, National's 2017 election majority of 4817 should be impregnable, but a local poll last month put Labour's Kiri Allan ahead of new National candidate Tania Tapsell.

Former National Cabinet minister Anne Tolley is stepping down after holding the seat since 2005.

Allan, a sitting list MP, and Tapsell, a Rotorua councillor, are both Māori women standing in a region where Māori make up about half the population - although many are on the Māori rolls.

With 58 per cent of the vote counted, Allan is well ahead with 15,192 votes to Tapsell's 10,924.

Hamilton East

Like East Coast, Hamilton East's National majority of 5810 votes last time should make it safe for National in any normal year. This may, however, not be a normal year.

Once again National's David Bennett faces a challenge from Jamie Strange, who has been a Labour list MP since 2017.

At 8pm Labour candidates are ahead in both Hamilton East, where Strange leads by 2213 votes, and in Hamilton West, where Labour's Gaurav Sharma is 3817 votes ahead of National's Tim Macindoe.

Takanini

Takanini is a completely new electorate being contested for the first time. It is mostly made up of Judith Collins' old Papakura electorate, and smaller portions of the Manurewa and Hunua electorates.

Analysis of 2017 general election data suggests it is "light blue" - likely to have a slight National majority. However, that does not take into account Labour's huge growth in popularity in the last three years, which could make the contest very close.

Both National's candidate, lawyer and businesswoman Rima Nakhle, and the Labour candidate, GP Neru Leavasa, are first-timers.

One factor on National's side is that Nakhle is being helped by Auckland councillor Daniel Newman, a close associate of Collins who is considered one of the best campaigners in the city.

The electorate is also being contested by Elliott Ikilei, deputy leader of New Conservatives, who could steal a few of National's more conservative or hard-right voters.

With 60 per cent of the vote counted, Labour's Leavasa is ahead by 3307 votes.

Māori Party hopes

Tāmaki Makaurau

The Māori Party needs to win an electorate to get back into Parliament this year. It has been arguing that the sitting Labour MPs in all seven Māori seats are sure to get back on the Labour Party list anyway, so voters can get two MPs for the price of one by giving their electorate votes for the Māori Party.

A poll this week in the Auckland seat of Tāmaki Makaurau suggested that the strategy might be paying off for party co-leader John Tamihere, who was polling just 6 points behind sitting Labour MP Peeni Henare.

With almost half the vote counted, Henare is still ahead by 828 votes.

Te Tai Hauāuru

The other Māori Party co-leader, Debbie Ngarewa-Packer, is also reckoned to be in with a good chance of winning back the old Western Māori seat, Te Tai Hauāuru, previously held by party co-founder Tariana Turia from 2002 to 2014.

Current Labour MP Adrian Rurawhe is one of Labour's lowest-profile Māori MPs, although his family links as a great-grandson of Ratana Church founder T W Ratana give him local mana.

With just over half the vote counted, Rurawhe is narrowly holding the seat by 572 votes.

Waiariki

Waiariki was the last seat held by the Māori Party, and its previous co-leader Te Ururoa Flavell lost by just 1719 votes to Labour's Tamati Coffey in one of the biggest election-night upsets in 2017.

Labour's 2014 candidate for the seat, Rawiri Waititi, is standing this time for the Māori Party. A poll on October 4 found him trailing Coffey by 26 per cent to 38 per cent.

Vision NZ leader Hannah Tamaki, who is also standing in the seat, registered only 2 per cent in the poll, but 24 per cent of voters were still undecided.

Coffey stayed ahead through most of the night, but Waititi has pulled marginally ahead by 36 votes with 66 per cent of the vote counted by 9.50pm.

Northland - NZ First's hope

NZ First leader Winston Peters triumphed in the Northland electorate in a 2015 byelection, when voters could afford to take a punt knowing that it would not threaten John Key's National Government.

In 2017, when it mattered, Northland voters returned to National - but only just. National MP Matt King holds a slim margin of just 1389 votes.

Peters has passed the NZ First standard this year to Shane Jones, who is widely assumed to be the next party leader when Peters eventually retires.

National's King is just 348 votes ahead of Labour's Willow-Jean Prime with 46 per cent of the vote counted, with Jones running a distant third.

National's wish list

Ōhāriu

Former police union boss and Ōhāriu MP Greg O'Connor says it's "all or nothing" as he bids to defend one of the country's most marginal seats - which has a surprise new contender.

O'Connor has taken himself off the Labour Party list, meaning if he falls to National MP Brett Hudson, he'll be out of Parliament.

He won the wealthy Wellington electorate by just 1051 votes in 2017, after 33-year representative and United Future Peter Dunne quit the campaign only two weeks before the election and as Jacinda Ardern turned around her party's fortunes.

With two-thirds of the vote counted, O'Connor is comfortably holding the seat with a margin of 9312 votes.

New Lynn

Labour has held New Lynn since it was created in 1963, but the race this year could be closer than any other. Changes to the electorate's boundary mean that, on paper, the seat has become marginal. The electorate has now absorbed parts of West Auckland which used to be in the National-majority Helensville electorate.

But that is on paper, and 2020 is a very different election to 2017, given Labour's rise in popularity.

Labour's Dr Deborah Russell won the seat in 2017 by 2800 votes. Lisa Whyte, the National candidate and local board member, is low profile and is ranked at 49th on National's list, which means she is likely to need to win the seat to get into Parliament.

Russell is riding the Labour wave with a massive 9149-vote margin over Whyte with 60 per cent of the vote counted.

Te Atatū

Labour MP Phil Twyford has been growing a comfortable majority in Te Atatū over the last two elections.

Phil Twyford (right), pictured with Roseridge Rest Home resident Dominic Claffery, is saddled with the failures of KiwiBuild and light rail. Photo / Steve Braunias

But as a minister, his failures have been large and high-profile. KiwiBuild has been this Government's most glaring failure, and he lost his housing portfolio because of it. Light rail in Auckland, a key part of his transport portfolio, has also stalled.

Voters are choosing between a high-ranking minister who still has significant power in Cabinet, and a National Party backbencher whose stocks appear to be falling. Alfred Ngaro was demoted by Judith Collins in National's list rankings from 20 to 30, meaning he may need to win the seat to survive as an MP.

Ngaro has also had a bumpy parliamentary term. He briefly considered breaking away from National to form a new Christian party, before deciding to stay.

Twyford is heading off Ngaro with a 4023 margin with 39 per cent of the votes counted.

Banks Peninsula

Last election Labour stalwart Ruth Dyson won Port Hills by a massive 7916 votes, but
Dyson's retirement and boundary changes creating the new seat of Banks Peninsula could make the contest more marginal.

Labour has selected Tracey McLellan, the party's senior vice-president and organiser with the NZ Nurses Organisation. McLellan holds a PhD in psychology and worked for some time in clinical research into dementia and childhood brain injury.

National's candidate is Catherine Chu, an identical twin who started university at 15 and began her career in private banking at 18.

With two-thirds of votes counted, McLellan is a huge 10,286 votes ahead.

Taieri

The old Dunedin South seat was safely Labour with a 2017 majority of 8717 for Labour's Clare Curran. But boundary changes have brought in a big chunk of National-voting rural areas, changing the seat's name to Taieri.

Labour has chosen former lawyer, TV3 journalist and director of the British Council NZ, Ingrid Leary, who moved to Dunedin late last year from Waiheke.

National's candidate is Liam Kernaghan, who previously worked in Wellington as a political adviser to Amy Adams and Simon Bridges.

O'Leary leads Kernaghan by a margin of 4993 with 64 per cent of the vote counted.