A guide to Turkey's pivotal election

Turkey on Sunday votes in presidential and parliamentary elections that will pass judgement on two decades of uninterrupted rule by Recep Tayyip Erdogan and his Islamic-rooted party.

AFP looks at the key points of a vote with ramifications across the globe.

Erdogan is aiming to extend his transformative grip on power, which started when he became prime minister in 2003 after a landslide election victory for his conservative Justice and Development Party (AKP) the previous year.

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The 69-year-old could remain at the helm of the Turkish state until 2028 if re-elected, after the two-term limit for presidents was reset in a 2017 constitutional change.

His main challenger is Kemal Kilicdaroglu, leader of the secular Republican People's Party (CHP) and head of a disparate six-party alliance whose main unifying point is ousting Erdogan.

Polling suggests the 74-year-old former civil servant has a chance of reaching the 50-percent threshold needed for a first-round win and to avoid a May 28 runoff.

A third candidate, nationalist Sinan Ogan, is expected to win a small fraction of votes and believed to be drawing more support away from Erdogan.

The 2018 election runner-up Muharrem Ince dramatically announced his withdrawal from the race on Thursday -- although his name will appear on the ballot papers anyway.

Voters will also select 600 members of parliament from 87 electoral districts to represent them in Turkey's unicameral parliament for the next five years.

The AKP is the largest party in the legislature and commands a majority in an alliance with the far-right Nationalist Movement Party (MHP).

The CHP -- founded by Mustafa Kemal Ataturk, the father of the modern Turkish republic born out of the Ottoman empire's ashes in 1923 -- is the leading opposition group.

The pro-Kurdish Peoples' Democratic Party (HDP) is parliament's third-largest, representing a community that makes up roughly one-fifth of Turkey's population.

Parliament's powers were severely weakened after Erdogan won a 2017 constitutional referendum that abolished the post of prime minister and enabled the president to effectively rule by decree.

Kilicdaroglu has pledged to restore powers to the legislature and limit the president to one seven-year term if he wins.

But he would need an unlikely three-fifths parliamentary majority to enact such changes.

More than 64 million of Turkey's 85 million-strong population are eligible to cast a ballot on Sunday. Turnout rates have been high in the past, exceeding 86 percent.

Polls open at 8:00 am (0500 GMT) and close at 5:00 pm.

Around 5.2 million Turks, having celebrated their 18th birthday, will participate in a national election for the first time.

Polling suggests this voting group -- representing eight percent of the electorate -- will reject the AKP as they tend to hold more liberal values and have known no leader other than Erdogan.

More than three million Turks living abroad have already cast their vote, with Germany alone accounting for nearly half of the diaspora electorate. These voters have usually backed conservative candidates.

The Organization for Security and Co-operation in Europe (OSCE) is deploying hundreds of observers, in addition to the hundreds of thousands of volunteers chosen by the parties.