Polls open at 7 am (0000 GMT) in what is expected to be an unusually close race between the incumbent, Purnama, the city's first Christian and ethnic Chinese leader, and a former education minister, Baswedan, a Muslim.
Millions of Indonesians head to the polls in Jakarta on Wednesday to choose between a Muslim and a Christian candidate for governor, as religious tensions run high in the capital of the world's third-largest democracy.
Polls open at 7 am (0000 GMT) in what is expected to be an unusually close race between the incumbent, Basuki "Ahok" Tjahaja Purnama – the city's first Christian and ethnic Chinese leader – and a former education minister, Anies Baswedan, who like 85 percent of Jakarta residents, is Muslim.
Security is also unusually tight for the poll. Police say about 66,000 personnel are deployed throughout the city of some 10 million people to prevent voter intimidation and civil unrest.
TRT World spoke to Jack Hewson in Jakarta about the elections.
Test for democracy
The election is viewed as a test for Indonesia's young democracy and record of religious tolerance. Given Jakarta's outsized importance as both the nation's capital and commercial centre, the election is also viewed as a barometer for a 2019 presidential election.
Purnama is backed by President Joko Widodo's ruling party.
Baswedan, is backed by a conservative retired general, Prabowo Subianto, who lost to Widodo in a 2014 presidential vote.
Several opinion surveys have showed the candidates in a statistical dead heat.
About seven million people are eligible to vote by 1 pm (0600 GMT), when polling stations close.
Private pollsters, approved by the national elections commission, are expected to announce an unofficial tabulation of a sample of votes, known as "quick counts" within a few hours of polls closing.
The elections commission is expected to announce official results by the first week of May.
The loser, however, can contest the results in Constitutional Court, which could prolong political uncertainty for weeks.
Citing security concerns, police on Monday blocked plans by thousands of members of hardline Islamic groups, including those from outside the city, to stand guard at polling booths.
Authorities in neighbouring provinces on Java island have urged the public to refrain from non-essential travel to Jakarta. Police in Central Java raided private cars and public buses on Tuesday for sharp objects and explosives.
Incumbent governor Purnama is on trial for blasphemy over comments he made last year that many took to be insulting to Islam. Hundreds of thousands of Muslims took to the streets late last year to call for his sacking and to urge voters against electing a non-Muslim leader.
Purnama faces up to five years in jail if convicted of blasphemy. His trial will resume on Thursday, when prosecutors will submit their sentence request.