Polling stations opened on Wednesday morning across Indonesia, the world's third largest democracy, for general elections which are pitting the incumbent president Joko Widodo against a former army general, Prabowo Subianto, in a repeat of the previous polls held in 2014.

The election campaign was a bitter affair in which nationalism and religion played prominent roles.

More than 190 million Indonesians will cast their votes at nearly 80,000 polling stations from 07:00 local time (22:00 GMT Tuesday) in the east of the country. They will close at 13:00 (06:00 GMT) in the west of the archipelago nation, where the capital Jakarta is located. The country has three time zones.

In addition to electing the president and vice president to five-year terms, voters will also appoint members of parliament to 575 seats in the lower house, 136 in the upper house and nearly 19,000 seats in the provincial and municipal legislative chambers.

It is the first time that Indonesia's presidential, parliamentary and local elections are taking place concurrently on the same day, with 192 million people spread across thousands of islands eligible to vote in what is one of the world's most complex single-day polls.

Another two million Indonesian nationals living abroad were expected to vote by mail, with postal votes being held last week.

A total of 16 political parties will be represented at the national level, 10 of which are part of the coalition led by Jokowi, as the current president is widely known, while five other parties support Prabowo.

Pre-election surveys predict a comfortable victory of about 20 percentage points for Jokowi, although some analysts have not ruled out a surprise result because of swing voters and possible polling errors.

The incumbent is part of the Indonesian Democratic Party of Struggle (PDI-P), led by former president Megawati Sukarnoputri, which holds 109 of the current 560 seats in Parliament, while Prabowo chairs the opposition Great Indonesia Movement Party (Gerindra), which currently has 73 seats.

Both candidates have employed nationalist and religious Islamic rhetoric during their campaigns and defended "Pancasila", the foundational philosophy of the Indonesian state which proclaims "Unity in Diversity", at their rallies.

Indonesia, the largest Muslim country in the world where 88 percent of the population practice Islam, has six major official religion and hundreds of ethnicities, languages and minority groups, spread across more than 17,000 islands.

However, activists and nonprofits have raised concerns over the politicization of Islam in the country and a rise in Islamic fundamentalism and conservatism in recent years.

Jokowi, who picked one of the most influential Islamic clerics, Ma'Ruf Amin as his running-mate, has based his campaign on continuity and pursuing social and development policies, while the former general has promised to restore greatness to Indonesia and enhance development by preventing the plundering of national resources by foreigners.

Preliminary election results will be made public on Wednesday soon after polling stations close, although official results will not be revealed until May.