Winner to be declared in South Australia by-election

Authorities will declare the winner of a by-election for the Adelaide seat of Fisher after a week of twists and turns.

Labor's Nat Cook is tipped to retain a slender two-party-preferred lead over the Liberals' Heidi Harris, giving Labor a majority in the lower house for the first time since the March election.

Independent candidate Daniel Woodyatt remains an outside chance to claim victory if he can secure enough preferences from minor parties and other independents.

The SA Electoral Commission will declare the winner on Saturday after counting the last batch of pre-poll votes and conducting a final distribution of preferences.

But a recount could be on the way, as the result is set to come down to just a handful of votes.