New Zealand First Party leader Winston Peters Speaks to media outside The Duke Of Marlborough Hotel in Russell the day after the Election.

ANALYSIS: There are almost 400,000 votes still to be counted in last night's general election - equivalent to 15 per cent of the total votes cast.

That could change the mix of seats the parties win but will almost certainly not affect the big picture - that both Labour and National need NZ First to form a government.

But it could have a fundamental impact on the way Peters looks at the choice he has to make - in particularly the stability of a Left bloc option.

JASON DORDAY/STUFF NZ First leader Winston Peters at The Duke Of Marlborough Hotel in Russell on election night. He may face a different mix of seats once special votes are counted.

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​In the past special votes have tended to favour the Left. Labour and the Greens are hopeful that they will swing a couple of seats their way, as they did in 2014.

Wellington legal blogger Graeme Edgeler has pointed out that in 2014 National did 17 per cent worse on special votes than they did with ordinary votes, while the Greens did 53 per cent better.

FIONA GOODALL/GETTY lMAGESl Special votes could change the picture as National's Bill English looks to negotiate a deal with NZ First.

Labour did 14 per cent better on special votes in 2014, than they did with ordinary votes.

If that was replicated this time that would cut National's total from 58 seats to 56 and list MPs Nicola Willis, who was unsuccessful in Wellington Central, and Agnes Loheni would miss out while Labour's Angie Warren-Clark and the Green's Golriz Ghahraman would be elected

That would not change the essential choice - between a National-led government supported by Winston Peters and NZ First or a Labour-Green-NZ First arrangement.

Labour's backroom guru and numbers man Rob Salmond on election night estimated Labour would improve from its 35.8 per cent to maybe 37 per cent while National would slide from 46.1 per cent down to 44 per cent.

At the moment if Peters throws his lot in with Labour and the Greens they would have a bare majority - 61 to 59 - and Peters may view that as too precarious to negotiate a full three year term.

But if two seats do change hand it would mean a National-NZ First government (with the support of ACT's one MP) would have 66 seats and the alternative Labour-led one 63 - a much safer bet for Peters because the government would be less "hostage to fortune".

The deadline for the count of special votes is 2pm on October 7 with the final declaration of the election result due on October 12.

That fits in with the timetable Peters has talked about, and means there will be no repeat of the six weeks of negotiation that followed a similar scenario in 1996 when Peters held the balance of power.

"I will not be giving any answers tonight or tomorrow until I've had a full chance to talk to our full board of New Zealand First, our supporters and organisations around the country and our MPs," Peters said on Saturday.

According to the Electoral Commission's estimate there are 384,072 "special declaration votes" (15 per cent of the total) including 61,375 overseas and dictation votes. The latter are cast by the blind or visually impaired people or those with a disability who need help to vote.

But crucially they include those voters who enrolled late - in the last two weeks before the election.

Labour and the Greens believe they will lean heavily their way because they are predominantly young - the Left's hoped for "youthquake" - that responded enthusiastically to Jacinda Ardern as the new Labour leader.