ISTANBUL – Turkish voters were casting their ballots Sunday in a historic referendum on whether to approve constitutional reforms that would greatly expand the powers of President Recep Tayyip Erdogan.
If the "yes" vote prevails Sunday, the 18 constitutional changes will replace Turkey's parliamentary system of government with a presidential one, abolishing the office of the prime minister.
Erdogan and his supporters say the "Turkish style" presidential system would bring stability and prosperity in a country rattled by last year's coup attempt and a series of devastating attacks by the Islamic State group and Kurdish militants.
But opponents fear the changes will lead to autocratic one-man rule, ensuring that Erdogan, who has been accused of repressing rights and freedoms, could govern until 2029 with few checks and balances.
Erdogan described the referendum as an opportunity for "change and transformation" as he voted in Istanbul, where black-clad bodyguards with automatic weapons stood guard outside the polling station.
"We need to make a decision that is beyond the ordinary," Erdogan said, adding he hoped Turkish voters would make the "expected" decision.
Kemal Kilicdaroglu, the leader of Turkey's main opposition party and top "no" campaigner, called it a vote on Turkey's fate.
"We hope the results will be good and together we can have the opportunity to discuss Turkey's other fundamental problems," he said.
Polls in eastern Turkey opened at 7 a.m. (0400 GMT) and were to close at 4 p.m. (1300 GMT), while those in the more populous west were opening and closing an hour later. More than 55 million people in this country of about 80 million are registered to vote.
People were already lined up at an Istanbul polling station before it opened.
"We are here early to say 'no' for our country, for our children and grandchildren," said retired tax officer Murtaza Ali Turgut. His wife Zeynep agreed, saying: "I was going to come sleep here last night to vote at first light."
Another "no" voter, Husnu Yahsi, said: "I don't want to get on a bus with no brake system. A one-man system is like that."
In another Istanbul neighborhood, a "yes" voter expressed full support of Erdogan. "Yes, yes, yes. Our leader is the gift of God to us. We will always support him. He's governing so well," Mualla Sengul said.
The official Anadolu news agency reported that military helicopters flew ballots and elections officers to some districts of Diyarbakir due to security reasons.
The proposed changes would grant the president powers to appoint ministers, senior government officials and half the members of Turkey's highest judicial body, as well as issue decrees and declare states of emergency. It sets a limit of two five-year terms for presidents and also allows the president to remain at the helm of a political party. The changes would come into effect with the next general elections, scheduled for 2019.
Erdogan, 63, first came to power in 2003 as prime minister and served in that role until becoming Turkey's first directly elected president in 2014. He has long sought to expand the powers of the president. The result of Sunday's referendum will determine Turkey's long-term political future and will likely have lasting effects on its relations with the European Union and the world.
Prime Minister Binali Yildirim, who leads the ruling Justice and Development Party, was nominated to lead the government in May after Ahmet Davutoglu stepped down amid differences with Erdogan. The president and Yildirim have been working closely and campaigned together for the "yes" vote.
The campaign has been highly divisive and heavily one-sided, with the "yes" side dominating the airwaves and billboards across the country. Supporters of the "no" vote have complained of an atmosphere of intimidation, with the main opposition party recording more than 100 incidents of obstruction to its campaign efforts, including beatings, detentions and threats.
The vote comes at a time when Turkey has been buffeted by problems. Erdogan survived a coup attempt last July, which he has blamed on his former ally and current nemesis Fethullah Gulen, an Islamic cleric living in the United States. A state of emergency imposed in the coup aftermath remains in effect. A widespread government crackdown has targeted followers of Gulen and other government opponents, branding them terrorists.
Roughly 100,000 people, including judges, teachers, academics, doctors, journalists and members of the military and police forces, have lost their jobs, and more than 40,000 have been arrested. Hundreds of media outlets and nongovernmental organizations have been shut down.
Turkey has also suffered renewed violence between Kurdish militants and security forces in the country's volatile southeast, as well as a string of bombings, some attributed to the Islamic State group, which is active across the border in Syria.
The war in Syria has led to some 3 million refugees crossing the border into Turkey. Turkey has sent troops into Syria to help opposition Syrian forces clear a border area from the threat posed by Islamic State militants.
Meanwhile, Turkey's relations with Europe have been increasingly tense, particularly after Erdogan branded Germany and the Netherlands as Nazis for not allowing Turkish ministers to campaign for the "yes" vote among expatriate Turks.
Suzan Fraser from Ankara, Bram Janssen in Istanbul and Mucahit Ceylan in Diyarbakir contributed to this report.