Labor has seized a historic victory in the South Australian election, despite a surging One Nation vote that decimated the Liberal Party’s statewide result.

A humbled Premier Peter Malinauskas said that although it was the best result his party has ever achieved, it was important that no one confused the result as adulation.

Labor had secured 30 seats, the Liberals four seats but the remaining 13 seats in the lower house were in doubt.

In a historic result, One Nation had a 19.2 per cent swing, while the Liberals vote collapsed with a 15.9 per cent swing against it, with nearly 40 per cent of the vote counted.

One Nation candidates were leading the primary vote in the lower house seats of Hammond, Mackillop and Ngadjuri, which would be decided on preferences.

One Nation Leader Pauline Hanson said it was unclear how many seats the party had won but pointed to state leader Cory Bernardi’s success in winning his upper house seat.

She said the party would be going hard for former federal Liberal leader Sussan Ley’s seat of Farrer and at the Victorian state election.

“There’s a movement. There’s an undercurrent, and it’s people saying we’ve had a gutful. We want our country back. We want to have a voice,” she told Sky News.

Bernardi said he was smiling.

“Because today an earthquake has rattled the foundations of uni-party politics in South Australia,” he said.

Liberal leader Ashton Hurn retained her seat in the Barossa Valley and will remain in the leadership role.

“Now is the time to celebrate the Liberals, the future, because there’s hope for the Liberal future here in South Australia,” she told supporters.

“The voters didn’t give us the nod this time, we’ll keep fighting into the future. The voters never get it wrong, and they’ve sent us a clear message.”

“The voters didn’t give us the nod this time, we’ll keep fighting into the future. The voters never get it wrong, and they’ve sent us a clear message.”

Federal Liberal senator Anne Ruston said the party had been sent a clear message and needed to return to the centre right.

She said the party could not win by moving to the right or the left.

At the Labor victory celebration, Malinauskas read a Henry Lawson poem, The Duty of Australians, and noted that our patriotism was “less brash and boastful and more dogged and determined”.

“Diversity has always been our greatest strength,” he said.

ABC election analyst Casey Briggs said the result was “the disintegration of the two party system”.

“It’s a political earthquake we’re watching in South Australia tonight,” he said.

“SA Labor has had its best result in the House of Assembly on record and at the same time we have a massive disruption on the right of politics.”

A record 454,862 (34.5 per cent) people cast early votes and 174,000 (13.2 per cent) requested postal ballots, meaning almost half the 1.3 million eligible voters had potentially voted before election day.

—AAP