Jokowi, the first Indonesian president from outside the military and political elite, announced his vice-presidential candidate, Ma'ruf Amin, on Thursday after weeks of fevered speculation in local media.

Jokowi's pick has become bigger news in Indonesia, the world's third-largest democracy, than an earthquake on the island of Lombok that killed more than 300 people.

Amin heads the influential Indonesian Ulema Council and the advisory council of Nahdlatul Ulama, the world's largest Muslim organisation.

Jokowi's pick disappointed liberals but analysts say it shores up his position among conservative Muslims who demonstrated their political power last year with the ouster of Jakarta's minority Christian governor who was later imprisoned for blasphemy.

Jokowi's opponent for a second time, nationalist politician and former general Prabowo Subianto, is running with businessman and deputy Jakarta governor Sandiaga Salahuddin Uno. They're expected to officially register as candidates after Friday prayers.

A longtime commander in Indonesia's "Kopassus" special forces, Subianto was discharged from the military in 1998 after Kopassus soldiers tortured activists who opposed dictator Suharto. Human rights groups allege he led a 1983 massacre in East Timor in which more than 300 people were killed.

There was a celebratory atmosphere and snarled traffic outside the election commission in central Jakarta as Jokowi and Amin arrived. After registering, Jokowi praised his opponents.

"Prabowo Subianto and Sandiaga Uno are the best sons of the nation like me and Mr. Ma'ruf Amin. They want to struggle for our beloved nation," he said.

The 2014 presidential election was marred by dirty campaigning and wild internet rumours that Jokowi was a secret communist and of Chinese background, accusations often used in Indonesia to discredit or intimidate political opponents.

Australian Associated Press