Opposition figures, however, vowed to challenge numerous ballots in the tight race.
President Recep Tayyip Erdogan has claimed victory in the vote, which looks set to grant him sweeping new powers.
The results from Sunday's vote are expected to have a huge effect on Turkey's long-term political future and on its relations with the European Union and the world. Although the result, if officially confirmed, would fall short of the sweeping victory Erdogan had sought, but nevertheless cements his hold on the country's governance.
"Yes, I voted and of course [I voted] No because Erdogan wants to be a dictator and he is not a democrat", said Sinan Beritan Mehmetoglu, whose mother, Sengul, the head of a social democratic Kurdish party in the eastern city of Kars, was detained by the authorities in December.
Turkey's Prime Minister Binali Yildirim, who voted in Izmir, told reporters: "Whatever the result may be, it will be highly respected by us". "Turkey has been ruled in the past by one man", he said, referring to modern Turkey's founder Mustafa Kemal Ataturk. In our democracy's history, a new page has opened with this vote.
But he urged people not to succumb to "lethargy" and go out and vote, saying "the stronger result the better".
Kemal Kilicdaroglu, leader of the main opposition Republican People's Party (CHP), said Turkey was at a crossroads between a democratic parliamentary system and a "one-man regime".
"There is the state on one side and people on the other".
Traditional AK Party supporters were helped over the line by backing from the right-wing Nationalist Movement Party, Turkey's smallest parliamentary party. CHP vice chairman Erdal Aksunger said they would challenge 37 percent of the ballot boxes. The changes will come into effect with the next general election, scheduled for 2019.
Erdogan is seeking to change Turkey's parliamentary system into an executive presidency, giving him more power to appoint cabinet ministers, choose judges, sign decrees and dissolve parliament.
Critics of the changes fear the move will make the president's position too powerful, arguing that it amounts to one-man rule, without the checks and balances of other presidential systems such as those in France and the US.
Mr Erdogan described the referendum as an opportunity for "change and transformation" as he voted in Istanbul, where bodyguards with automatic weapons stood guard outside the polling station. "And 90 percent of the Turkish media are right now under Erdogan's control, close to 100 media organizations have been shut down and nearly 200 Turkish journalists are in jail", the journalist said, adding that there is almost no one left to withstand his dictatorship. Voters use an official stamp to select between "yes" and "no" - the question itself is assumed to have been understood by all in advance.
Observers from the Organisation for Security and Co-operation in Europe (OSCE) monitored the voting process Sunday in the Turkish capital as the country headed to polling stations. "[Over] the past 70 years, we've had over 45 governments and that's due to the unstable political system", Yavuz said.
"The new constitution will bring stability and trust that is needed for our county to develop and grow", Erdogan told supporters Saturday in Istanbul's Tuzla district. "Yes, yes, yes. Our leader is the gift of God to us. He's governing so well".
Erdogan was voted to power in August 2014, the first time a Turkish President had been directly chosen by popular vote.
The referendum campaign was divisive and heavily one-sided, with the "yes" side dominating the airwaves and billboards across the country.
"This referendum differs from all previous elections in Turkey as it envisages the changes in the form of government", Erdogan told reporters April. 16.
He has initiated a widespread crackdown on opposition, which intensified after last year's botched coup, for which he blamed US-based cleric Fethullah Gulen.
The man was restrained and pinned down to the ground by police and civilians at the scene before being taken into investigation. Jerusalem's Hadassah Medical Center said the woman died soon after she was rushed there following the attack on Friday.
This morning it was discovered that Apple was on the list for road testing autonomous vehicle permits in California. There have been reports in the past year that Apple scaled back plans to build its own vehicle.
The woman, who is in her twenties, was then taken for further treatment to the Hadassah Medical Center, Mount Scopus. She was brought to the hospital in critical condition, with multiple stab wounds to the upper body, a medic said.
Bheka Ntuli from Durban said it was time South Africa sought a commited and passionate president who would listen to the masses. President Jacob Zuma on Monday described last week's protests demanding that he resign as racist.
A Gwinnett County police officer has been terminated after video of a traffic stop shows him stomp a handcuffed man on the head. A prosecutor in Georgia has dismissed dozens of cases involving two former officers fired in a police brutality case .
In 1997, the number 42 was retired across Major League Baseball and remains the only jersey number retired across the league. Jackie Robinson Day certainly won't heal America's divisions-or even baseball's divisions. "This is special", Maybin said.
As of Sunday, 10 of the 15 people wounded in the truck attack in the Swedish capital remained hospitalized, including one child. A fire broke out Friday afternoon at the store after the truck smashed into shoppers at its entrance on Drottninggatan street.
Another woman, who is pregnant, was injured when the train stopped, and a man was hurt while trying to flee the assailant. Later the city's Hadassah University Medical Center told the Jerusalem Post that Bladon had died of her wounds.
The restaurant will be closed for the Easter weekend because of the boy's death, CNN affiliate WGCL-TV in Atlanta reported. The child suffered critical injuries, however, and later died at the hospital, police said.
They sustain our peoples and their livelihoods. "And, the one that has attracted the greatest attention is the Teesta", he said. However, the pressing issues Bangladesh faces with India seem to have lost steam in the fanfare of this historic visit.
Speaking to 2FM's Game On, Dunphy said: "It's a bit of a mystery why Mourinho is so savage with him and repeatedly digs him out". But we've got a home game next, let's see if we can get some momentum, try to get a win in that and we'll try to do that".
McMaster: North Korea's provocations 'can't continue'
US Defense Secretary Jim Mattis said President Donald Trump had been briefed on the latest test but had "no further comment". Pacific Command said the missile "blew up nearly immediately", adding the type of missile was being analysed.
Celtics star Thomas' sister killed in auto accident
Saturday when it drifted off the road. "The thoughts & prayers of the entire organization are with Isaiah & his family". The accident reportedly occurred around 5 a.m. when Chyna Thomas' vehicle faded into the left shoulder of the highway.
Man City enjoy convincing win against Southampton
City are set to be without Bacary Sagna for the trip to Southampton - but skipper Vincent Kompany is pushing for a starting spot. The most recent game that took place in Manchester on October 23rd, previous year was a 1:1 draw and the latest meeting at St.
Russia vetoes UN resolution to condemn Syria chemical attack
Still, Mr Lavrov sought to put a positive spin on the talks with Mr Tillerson, saying they helped improve mutual understanding. Trump made the remark at a joint press conference with visiting NATO Secretary General Jens Stoltenberg at the White House.
Arsène Wenger defiant after 'damaging' loss to Crystal Palace
Arsene controls the footballing situation, he says he would tell us [his decision] "soon" and that it doesn't affect the team. Flamini made 246 appearances over two spells at Arsenal but is now concentrated on helping to keep Palace in the top-flight.
Canada introduces bill to legalize marijuana
Government ministers said they hoped to have cleared legal hurdles in time to implement the legal marijuana proposal by July 2018. If the law succeeds, Canada will be the second country in the world to legalize marijuana . "We're going to change that".
NCAA football recruiting changes at a glance
This portion of the legislation doesn't become effective until August 1 and will affect the class of 2019. Only the Collegiate Commissioners Association can create new National Letter of Intent signing periods.