A supporter during a "Yes" referendum campaign rally in Istanbul.
"The presidential system we are bringing with this constitutional change is necessary for the development, growth and stability of our nation", Erdogan said.
Presidential and legislative elections would be held at the same time.
The referendum comes amid troubled times for Turkey, which has been plagued by a string of bombings, renewed violence between the government forces and Kurdish rebels and a failed coup attempt in July that resulted in a state of emergency that remains in place. Few Turkish governments since have run the country effectively; none has truly adhered to the rule of law. Turkey is made up of 81 provinces, whose governors are directly appointed by Ankara. Hundreds of news outlets and non-governmental organizations have been shut down.
The changes will also grant authority to the President to issue decrees within the executive jurisdiction, declare a state of emergency and appoint public officials.
That is bad, not only for Turkey, but for just about everyone with interests in the region, given the country's economic power and historically strategic location as a bridge between East and West - particularly with Syria's civil war and the fight against so-called Islamic State raging on its border.
If the referendum is approved, the Parliament would have reduced oversight powers.
He has also frequently demonised opponents, saying that those who wanted to vote "No" were playing into the hands of the PKK and US-based Muslim cleric Fethullah Gulen, blamed for the failed July 15 coup. The president would also be allowed to retain ties to a political party. "If the president is not speaking out, if he acknowledges it, then what would be the decision of nationalists - who are against a federal structure and support a unitary one - be (in the referendum) in two days?" The pro-Kurdish Peoples' Democratic Party has been decimated, with its charismatic leftist leader, Selahattin Demirtas, now languishing in prison.
When countries like the Netherlands stopped Turkish ministers from campaigning on their soil last month, Erdogan accused them of Nazi practices, throwing a critical deal on halting the flow of migrants to Europe into jeopardy.
Assuming the referendum passes, most of the changes it contains won't take effect until the next set of elections, due in 2019. This referendum is their fourth trip to the polls since expatriates were permitted to vote in Turkish elections while overseas.
The "no" backers had no way to stop Erdogan from taking full advantage of the state apparatus as he campaigned for the amendments, invariably receiving more TV news coverage than Kilicdaroglu and other "no" campaigners.
Utko Cakirozer, a former editor of the opposition daily Cumhuriyet, who's now one of six parliament members from Eskisehir, had gone to the "In Heavy Demand" coffee house to cheer on the "no" campaign.
Erdogan said Turkey, a long-time candidate country to join the European Union, had been unduly left waiting outside the bloc. A rejection of Erdogan's proposed constitutional amendments would keep alive the prospect that once this president is no longer in office, Turkey can finally have a shot at curbing the power of its rulers and, perhaps someday, making way for representative, inclusive democracy.