Political veteran Prabowo, a former special forces commander, trounced his rivals, winning about 58 per cent of votes according to four pollsters, based on “quick count” ballots at samples of voting stations nationwide. The number of votes tallied ranged from about 86 per cent to 95 per cent by 10pm local time.

Appearing before supporters alongside his running mate, the incumbent president’s son Gibran Rakabuming Raka, Prabowo, 72, declared the outcome “a victory for all Indonesians”, in a rousing speech that drew roars and applause.

“We are grateful for the quick count results. All the calculation, all pollsters including those on our rivals’ side, the figures showed a Prabowo-Gibran win in one round,” he said.

“We will assemble a government consisting of the best sons and daughters of Indonesia.”

Rivals Anies Baswedan and Ganjar Pranowo trailed with about 25 per cent and 17 per cent respectively, according to the independent pollsters conducting the sample counts, which in previous elections have proven to be accurate.

A preliminary count by the election commission was far slower and showed Prabowo securing 57.7 per cent of votes with about six per cent of ballots recorded.

The contest pitted the two popular former governors against the pre-election frontrunner Prabowo, who was feared in the 1990s as a top lieutenant of Indonesia’s late strongman ruler Suharto.

Crucially, Prabowo has the tacit backing of the wildly popular incumbent Joko Widodo, who is betting on his former rival as a continuity candidate to preserve his legacy, including the inclusion of his 36-year-old son Gibran on the ticket.

Anies and Ganjar urged the public not to draw conclusions on the outcome and to await the official result, which is expected by March 20 at the latest.

Their campaign teams said they were investigating reports of electoral violations, both calling it “structural, systematic and massive fraud”. They did not provide evidence.

To win in a single round, a candidate needs more than 50 per cent of votes cast and at least 20 per cent of the ballot in half of the country’s provinces. If no candidate wins a majority, a runoff between the top two finishers will be held in June.

The world’s biggest single-day election saw nearly 259,000 candidates vie for 20,600 posts across the archipelago of 17,000 islands. In the legislative contest, a coalition of parties backing Prabowo had about 42 per cent of votes, while an alliance behind rival Anies had 27 per cent, indicating a potential Prabowo government could have strong parliamentary backing.

But top billing on Wednesday was always the race to replace Jokowi, as the incumbent is known, whose influence could be the decisive factor in who takes the helm of a resource-rich Group of 20 economy of at least $US1.3 trillion ($A2 trillion).

Jokowi has reached his limit of two terms and had not explicitly backed a candidate, but he made highly publicised appearances with Prabowo at state events.

Since his 2019 run for presidency, Prabowo has transformed his image into a cuddly, cat-loving grandfatherly figure, attracting a huge youth following on social media in a country where more than half of the nearly 205 million electorate is under 40.

Prabowo said those were his key supporters.

Ganjar remained upbeat on Wednesday, but said his camp would investigate reports of fraud, which he did not detail.

“All the witnesses, all the parties, they are now working and no struggle is in vain. And of course everyone is still enthusiastic,” he said.

Anies’ camp said it had found many violations and cheating by village-level and government officials and police. It did not cite evidence but said its findings had been recorded.

But political analysts said the margin of Prabowo’s lead in the unofficial counts would make it difficult for rivals to launch a viable challenge.