Political leaders have cast their ballots in South Australia’s election, a significant event drawing nationwide attention due to its potential to reshape the traditional two-party landscape.

Projections suggest a clear victory for Labor in Saturday’s election, although opinion polls indicate that One Nation is polling between 22 and 28 percent, surpassing the Liberal vote, which stands between 14 and 20 percent.

Premier Peter Malinauskas spent nearly an hour in line at a polling station in his Croydon constituency on Saturday morning. Accompanying him were his wife Annabel and their children, Jack, George, Eliza, and Sophie.

Malinauskas mentioned that he adhered to his usual election day routine, starting with a run before heading to the Woodville Gardens polling booth with his family.

“This is the first time I’ve voted with four kids, and it comes with its own set of challenges,” he remarked.

The premier’s four young children displayed patience while waiting in the voting queue, though they were understandably tired by the time their parents reached the ballot box.

They were rewarded soon after with democracy sausages, with their father telling them “team Mali, dad’s got to go and do some work” as he rushed off for an appearance with Prime Minister Anthony Albanese.

Liberal leader Ashton Hurn voted at Angaston Town Hall in her Barossa Valley electorate of Schubert before heading to Adelaide to visit other booths.

One Nation leader Cory Bernardi cast his vote before election day.

Bernardi was among the record 454,862 (34.5 per cent) South Australians who cast their ballots at early voting centres, which opened a week ago.

Another 174,000 (13.2 per cent) had requested postal ballots, meaning almost half the 1.3 million eligible voters had potentially voted before election day.

In a final opinion poll released on Friday, YouGov forecast a 59-41 win for Labor on a two-party preferred basis against both the Liberals and One Nation – a 4.4 per cent swing in its favour.

YouGov’s Paul Smith said Labor was set to secure its largest two-party preferred vote in SA history, while the Liberals were on track for 19 per cent, their worst result in any state or federal election since the coalition was formed.

Liberal leader Ashton Hurn took over the role just 103 days before the election.

“One Nation’s surge to 22 per cent places them second in the state for the first time, with particularly strong support in regional areas,” he said.

Adelaide University emeritus professor of politics Clem Macintyre said the rise and rise of One Nation had the potential to create a watershed moment in Australian politics, and the end of two-party politics at a federal level.

“If they do make a breakthrough, they’re going to have to work hard to be a more serious and viable alternative government,” he said.

“It’s more frustration with the major parties … I think we can still say One Nation is a party of disaffected voters.”

Flinders University public policy associate lecturer Josh Sunman said One Nation’s discipline had been the surprise story of the campaign.

SA Premier Peter Malinauskas is poised to lead Labor to a historic victory.

He said One Nation had delivered targeted messaging and candidate discipline, and “I was expecting a lot more candidate scandals and meltdowns”.

Hours after he commented, a UK court issued an arrest warrant for One Nation’s Aoi Baxter over a charge of sexually touching a woman without consent, and he was swiftly disendorsed.

The state’s 600 polling booths are open from 8am to 6pm, when counting begins.

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