Special votes will separate Christchurch Central, after a dead heat in that electorate.
Both National's Nicky Wagner and Labour's Brendon Burns registered 10,493 votes.
The seat is traditionally a Labour stronghold, but there has been no difference when the 23,813 votes cast today were counted up.
The result will now be settled by the 3717 special votes which are still to be counted.
Green candidate David Moorhouse came a distant third with 3725 votes.