JAKARTA - Indonesia's President Joko Widodo has, as expected, defeated his old rival Prabowo Subianto at the polls again - this time by more than double the votes he had garnered at their last presidential race in 2014.

The President, best known by his moniker Jokowi, won 55.5 per cent of the votes against his opponent's 44.5 per cent, according to the final tally of ballots announced in the wee hours of Tuesday (May 21) morning by the elections commission (KPU).

Mr Joko and his vice-presidential candidate Ma'ruf Amin received 85,607,362 of the votes, or 11 percentage points more than the 68,650,239 votes cast for Mr Prabowo and his running-mate Sandiaga Uno, said KPU commissioner Evi Novida Ginting Manik after an extended plenary meeting.

A surprisingly high turn-out of almost 80 per cent of the 192.3 million eligible voters at the elections last month, also contributed to a wide margin of victory for the President.

Mr Joko's winning margin of 16.9 million votes this time round, is twice the 8.4 million voters who formed his lead over Mr Prabowo when he was first elected to office five years ago - reinforcing his growing popularity as a reformist leader, after a long and divisive election campaign.

The President garnered more votes than Mr Prabowo in 21 out of 34 provinces, including in Central Java and East Java, although his rival managed to retain his strongholds in West Java, Aceh and Banten.

Barring any legal challenge of the final KPU results, Mr Joko and Dr Ma'ruf will be declared the winners of the 2019 presidential election in the days ahead.

The official vote count, released a day ahead of schedule, comes amid heightened tensions in the capital Jakarta following plans by Islamist groups to mount protests against the results at the KPU headquarters.

It also follows warnings by Indonesian police of a possible attack by terrorists loyal to the Islamic State in Iraq and Syria (ISIS), who may be targeting its officers as well as people attending the street rallies.

Still, tens of thousands are expected to throng the streets around the KPU in downtown Jakarta to join a rally planned at the time when Muslim break their fast on Tuesday in the midst of Ramadan.

The rally organisers, who identified themselves as Persaudaraan Alumni 212, are calling the mass gathering a "constitutional jihad", according to publicity material seen by The Straits Times on Sunday.

The name Persaudaraan Alumni 212 refers to people who took part in a rally held in the capital more than two years ago on Dec 2, against former Jakarta governor Basuki Tjahaja Purnama for insulting Islam.

The 2016 protest, led by far-right Muslims from the Islamic Defenders Front, better known locally as the FPI, had threatened to destabilise the country during the gubernatorial election, which was marred by religiosity and sectarianism.

Many Islamist groups in Indonesia are known to back Mr Prabowo and Mr Sandiaga, while other supporters of the two have openly advocated a "people power" movement to delegitimise the KPU results.

Mr Prabowo's campaign team, however, has tried to distance themselves from the mob, including denying reports that the former general will be leading the rally on Tuesday.

The police and military have mobilised more than 32,000 security personnel in the city, hoping that a show of force will discourage any escalation of unrest or prevent a terrorist attack.

All eyes are now on Mr Prabowo and what his next course of action will be, as the elections commission takes a three-day time-out required by law to allow disputes of its results to be filed in court before it can officially announce the winners.

Mr Prabowo, who had claimed victory just hours after polls closed on Election Day, has been adamant that he will not accept the KPU results if it does not go his way.

He has also repeatedly said that the election was rigged in favour of the incumbent, amid other allegations of electoral fraud.

On Monday, Indonesia's elections supervisory body Bawaslu rejected a report filed by his campaign team accusing Mr Joko of vote-buying, among other allegations of systemic campaign violations.

Bawaslu, explaining its decision on Monday, said it had dismissed the allegations on grounds of weak evidence, specifically that the complainants submitted only news links from the Internet as proof.

They also did not meet the criteria that any alleged wrongdoing had affected at least half of the electorates in the 34 provinces across Indonesia, added the elections watchdog.

With Mr Prabowo's aides having ruled out taking their case to the Constitutional Court, which they had claimed would be a "waste of time", Indonesia will have to remain on tenterhooks for some time more, while he explores his options.