The vote, in which millions of Turks will decide whether to replace their parliamentary democracy with an all-powerful presidency, may bring the biggest change in their system of governance since the modern Turkish republic was founded nearly a century ago.
President Recep Tayyip Erdogan, who delivered a speech to a crowd in an Istanbul neighborhood, has long championed the idea of changing Turkey's system of government from parliamentary to presidential. He also appealed to voters of other parties to approve the changes so "Turkey can leap into the future".
On April 16, the electorate in Turkey will be asked to vote Yes or No to an 18-article reform bill, which would also change the current parliamentary system to a presidential one. Is it a "yes" for one homeland?
The role of the military is entwined in modern Turkish history but there are fears Turkey could lurch towards authoritarian rule following a crackdown on the power of the armed forces by President Erdogan after last year's pivotal failed coup.
If passed, the new presidential system will implement the most radical political shake-up since the fall of the Ottoman Empire, dispensing with the office of the prime minister and centralising the entire executive bureaucracy under the presidency.
"Turkey is at a junction".
Fatih Tuna, Istanbul AK Party Vice Chairman, said: "Even though the economy has improved there was still a coup attempt and we don't want to have to face this every 15 years". "We will make our choices with our children and future in mind", he said during his final rally in the capital Ankara.
The opposition has complained about an unfair campaign process, with Erdogan and the "yes" propaganda dominating air waves and billboards using state resources.
"Sunday will be a turning point in the fight against terrorism", he said.
Erdogan has painted supporters of the "no" campaign as people bent on destabilizing the nation, accusing them of siding with those blamed for the July 2016 attempted coup. More than 100,000 people have been fired or arrested, including more than 100 journalists.
Supporters see the new system as an essential modernisation step for Turkey to streamline government.
Among the experts who have voiced concerns about the deteriorating human rights situation in Turkey are Philip Alston, special rapporteur on extreme poverty and human rights; David Kaye, special rapporteur on the promotion and protection of the right to freedom of opinion and expression; Maina Kiai, special rapporteur on the rights to freedom of peaceful assembly and of association; and Koumbou Boly Barry, special rapporteur on the right to education.
City and town officials belonging to the Kurdish People's Democratic Party have been ousted from their positions and hundreds of its local leaders have been detained, the party said April 7.
More than 33,500 police officers will be on duty in Istanbul alone on referendum day, according to Turkish media. The Islamic State group has called for attacks against the referendum.
Never in recent times has Turkey, one of only two Muslim members of the North Atlantic Treaty Organisation military alliance, been so central to world affairs, from the fight against Daesh in Syria and Iraq, to Europe's migrant crisis and Ankara's shifting allegiances with Moscow and Washington.