Turkish President Recep Tayyip Erdogan claimed to have won a major victory in the referendum to grant the presidency greater powers Sunday.
With 98% of the ballots counted, 51.3% of voters voted "Yes" to the reform, compared to 48.7% who voted "no."
Erdogan has reportedly begun
Erdogan's supporters say that giving the presidency greater powers at the expense of the parliamentary system is necessary to modernize the country, while opponents view the reform as a power grab and an assault on democracy.
The opposition Republican People's Party (CHP) has already demanded a recount of 60% of the votes following the decision to accept unstamped ballot papers as valid unless they are proven to be invalid.
Deputy Prime Minister Veysi Kaynak said that the "Yes" vote was lower than expected despite being ahead.
The new system would concentrate the bureaucratic power in the hands of the president, aboloshing the role of the prime minister. Opponents fear that the reform could leave Erdogan in power until 2029.
Three people were killed in a shooting at a polling station in the south-eastern province of Diyarbakir.