By Sunday's end Turkey is expected to have a clear winner in the election runoff and what marks a historic first of a vote which went to a second, final round to decide the nation's president.

Earlier in the day incumbent President Recep Tayyip Erdogan cast his vote in Istanbul, while main challenger Kemal Kilicdaroglu voted in Ankara. The likely result is expected to be Erdogan securing a third term in office, given his performance in the first round, and crucially given Turkish nationalist candidate Sinan Ogan - who faired better than expected among the opposition - has now endorsed Erdogan for president. A by many accounts low turnout and lack of general enthusiasm for this second round is also a climate that favors incumbent Erdogan.

The May 14 first round vote saw Erdogan finish with a nearly five-point lead, but barely short of the 50% threshold required to win. On Sunday Erdogan said, "This is a first in Turkish democratic history" while casting his ballot.

"Turkey, with nearly 90% participation in the last round, showed its democratic struggle beautifully and I believe it will do the same again today," he added.

Through the opening hours of voting there were accusations of irregularities and issues in various places, which is not unusual in a Turkish national election. Some local reports have claimed attacks on ballot observers, and one report of a deceased person listed as eligible to vote.

Additionally, Istanbul’s chief public prosecutor has announced an investigation into social media accounts spreading 'disinformation' just ahead of polls opening. 

While more than 60 million people are registered to vote, one regional outlet - Middle East Eye - has observed turnout appears low and slow so far. This favors the incumbent. 

Kilicdaroglu's team has picked up on this, with the candidate tweeting for those who haven't voted to "go to the ballot box" and not be "lazy". He said the country's future is on the line and is "as close as walking distance". 

Below is a quick primer and timetable of what to expect Sunday, compiled by Al Jazeera: