It was a high-stakes litmus test at the midway point of the South Australian political term.

But more than 24 hours after polling booths closed in the Dunstan by-election, voters are yet to officially find out who will succeed the state’s former premier, Steven Marshall, in the state’s most marginal seat.

With about half the votes counted so far, Labor candidate Cressida O’Hanlon is poised to snatch Dunstan from the Liberals, polling 53.8 per cent of two-party preferred votes over Liberal Anna Finizio’s 46.2 per cent.

Labor’s likelihood of victory is strengthened by a significant surge in support for the Greens, whose preferences are likely to heavily favour the governing party.

So, why hasn’t the SA Electoral Commission declared a result?

Labor’s Cressida O’Hanlon (centre) is set to claim the seat from the Liberals.(ABC News: Trent Murphy)

One quarter of votes yet to be counted

In recent years, an increasing number of people have cast postal or early votes in state and federal elections.

The Dunstan by-election was no exception, with about 8,000 electors – more than one quarter of the total number of constituents in the seat – voting before polling day.

Unlike other Australian jurisdictions, pre-poll and postal votes cannot be counted on election night in SA. Instead, they must be counted on the Monday after polling day.

The SA Electoral Commission states early votes need to be securely transported to its processing centre, sorted, and then counted.

It says it also needs to allow seven days after polling day to receive all votes sent in the mail.

That means it could take days for the Electoral Commission to officially declare a result in Dunstan.

Voters are increasingly casting postal or early votes in state and federal elections which means it can take longer for the Electoral Commission to declare a result.(ABC News: Che Chorley)

Postal, early votes could sway election result

While a Labor win at the Dunstan by-election could bolster the government’s majority in the SA Parliament’s Lower House, a Liberal loss could further dent its prospects of success at the 2026 state election, and prompt speculation about its leader David Speirs’ future.

Liberal members are watching the pre-poll and postal vote count closely to see if the results impact Labor’s swing – currently sitting at 4.4 per cent.

Liberal candidate for Dunstan Anna Finizio faces an “exceptionally difficult” challenge, the party’s leader said.(ABC News: Che Chorley)

The party did not concede defeat on Saturday night, with Mr Speirs instead telling party faithful that there was a “pathway to holding the seat”.

“It is a pathway which has a lot of barriers in it and so that’s going to be challenging” he said.

“For that result I apologise. I am really sorry that it is as difficult as it might be.”

Meanwhile, Labor is yet to claim victory, with Premier Peter Malinauskas instead telling reporters on Sunday that Ms O’Hanlon was “on the cusp of achieving something quite special”.

“Although… we’re not claiming victory, quite the opposite, we are really excited about the opportunity we’ve got before us,” he said.

Labor candidate for Dunstan Cressida O’Hanlon is on the verge of a potentially “remarkable” result, the premier said.(ABC News: Che Chorley)

Call for SA electoral system to ‘catch up’ with voting trends

The SA Electoral Commission and Liberal Party had previously called for pre-poll votes to be counted sooner, to avoid drawn-out election counts.

Mr Malinauskas said the government planned to introduce legislative changes to Parliament before the 2026 state election to allow a quicker count.

“Postal votes and pre-polls have become part of the electoral system and I think the system has to catch up with that in the way the counting occurs,” he said on Saturday.

“The people of Dunstan want to know who their MP is and now they have to wait another 24 hours [which] seems crazy.

“That can be fixed and that’s something that we are committed to doing and hopefully it’s something that might enjoy bipartisan support.”

An electoral official with ballots during the Dunstan by-election count.(ABC News: Che Chorley)

SA Voice election results also yet to be declared

Meanwhile, the Electoral Commission will start counting votes from last weekend’s inaugural SA First Nations Voice to Parliament election this morning, with the count likely to take three days.

The Electoral Commission states the Voice election counting process was “complex” and several different steps needed to be completed.

Commissioner Mick Sherry told the ABC earlier this month that the independent body also needed to wait for the return of postal votes from rural and remote communities.

The commission will start counting votes for the Far North and Flinders and Upper North Local Voices today.

Votes for the four other Local Voices will be counted on Tuesday and Wednesday.

The commission expects to declare the results for each Local Voice before Easter.