Turkish President Recep Tayyip Erdogan has claimed victory in the referendum on granting him sweeping new powers, saying it was won by a clear majority.
He was speaking in Istanbul as the count neared completion.
With more than 99% of ballots counted, “Yes” was on 51.36% and “No” on 48.64%, reports BBC.
Erdogan supporters say replacing the parliamentary system with an executive presidency will modernise the country.
The two main opposition parties are challenging the results.
As jubilant Erdogan supporters rallied in the big cities, pots and pans were banged in Istanbul by opponents of the referendum, in a traditional form of protest.
If confirmed, the “Yes” vote could also see Erdogan remain in office until 2029.
BBC reports that three people were shot dead near a polling station in the south-eastern province of Diyarbakir, reportedly during a dispute over how they were voting.
If the Constitutional amendment bill is passed, what will change
If passed, CNN say the measures will represent the biggest constitutional upheaval in the country since its foundation in 1923 after the demise of the Ottoman Empire.
They would cement Erdogan’s grip on a country whose divisions have deepened since a failed coup attempt last July that ended with the deaths of more than 250 people and led to the imposition of a fierce crackdown on dissent.
Those who support the reforms believe they will kick-start a lethargic economy and stabilize a nation dealing with the resurgence of a 30-year conflict with militants from the Kurdistan Workers Party (PKK).
But opponents argue the proposals will lead to the formation of a constitutional dictatorship.
If Erdogan prevails in the vote, his grip on power would be considerably tightened. Term limits for the presidency would be reset and, if he wins elections in 2019 and 2024, he could be in power until 2029.
After serving as Prime Minster for more a decade, Erdogan became President in 2014.