Returns broadcast by state-run news agency Anadolu showed that with nearly all the votes counted, the "Yes" vote, in favor of the sweeping changes, had about 51.3 percent compared to 48.7 percent for the "No" vote.
Opponents of Turkey's controversial referendum to expand the powers of President Recep Tayyip Erdogan vowed to challenge the result Sunday, after he claimed victory for the "yes" vote by the slimmest of margins.
According to the preliminary data, as many as 51.3% of voters (or 1.3 million) supported the constitutional amendments replacing the country's parliamentary system with an executive presidency and eliminating the position of prime minister.
Nevertheless, thousands of flag-waving supporters rallied in Ankara and Istanbul in celebration.
There were scattered protests against the result, but these were more sporadic.
Supporters of the referendum say it's a justified change given the "existential threat" on the country's southern borders with Iraq and Syria, along with last summer's attempted coup, Han says. "It's too late now".
They also voiced hope the new path would help consolidate gains made in Turkey in the past 15 years for stability and prosperity and pave the way for continued accelerated progress of the Turkish people in the future.
He also took a dig at global critics.
"We would like other countries and institutions to show respect to the decision of the nation".
But voting patterns showed Turkey deeply divided over the changes, with the "No" vote victorious in the country's three biggest cities.
Turkey's main opposition Republican People's Party (CHP) had been campaigning for a "no" vote, against the proposed changes.
Turnover exceeded 80% with 53.561 million people voting in 176,140 ballot boxes in addition to 461 voting boxes for prisoners.
"The Higher Election Board has thrown a shadow on the people's decision".
It also stressed the importance of the political talks between Turkey and the European Union regarding the implementation of the constitutional changes.
The party has said it will contest the result of the referendum.
Turkey's main opposition party, known by its Turkish acronym CHP, has called for the results to be nullified, citing irregularities.
It's hard to overstate the incredible transformation of Turkey over the last decade under Erdogan's rule.
Initial reaction from overseas was cautious.
The Turkish referendum fell short of European standards, global observers say.
The referendum on Sunday night followed remarks from the Organisation for Security and Cooperation in Europe, of which Turkey is a member, that the conditions for the vote did not appear "fair".
"Even though I choose "no" and the results came out "yes", I wish the best to our country", he said.
Representatives from a coalition of worldwide bodies said the referendum took place on an "unlevel playing field" with the "yes" campaign dominating media coverage. The AP reports that supporters of the "yes" vote have dominated the airwaves, while supporters of the "no" vote have complained of intimidation. He imposed a very restrictive environment for the "no" camp. "I will feel more secure economically", says 26-year-old lawyer Mustafa Baskara.