Turks have voted on constitutional changes that could reshape the judiciary and curb the powers of the military, in a referendum seen as a tussle between an Islamist-influenced government and its secular opponents, mainly in the army.
Voting on 26 constitutional amendments began at 04:00 GMT on Sunday in the eastern provinces, and an hour later in the west. Polls closed at 14:00 GMT.
The referendum is seen as a crucial test for the governing Justice and Development Party (AKP), led by Recep Tayyip Erdogan, the prime minister.
Defeat could damage the AKP's morale before a parliamentary election due by July 2011.
Erdogan has said changes are needed to strengthen democracy and bring Turkey closer to European norms, as the country continues its bid to join the European Union (EU).
"Turkish democracy is at a turning point today, we are sitting an important test," Erdogan said after voting in Uskudar district of Istanbul.
Critics of the proposed overhaul from the "no" camp, say some of the changes would allow Erdogan's party to take over the courts, undermining the secular nature of the Turkish state.
"He [Erdogan] hoped that we uneducated people will say 'yes' ... He is transforming the constitution as it suits him. He wants to install his men everywhere," Fatma Uretici, a housewife who voted against the changes, said.
Some 50 million people are eligible to vote in the referendum that falls on the 30th anniversary of the 1980 military coup, which produced the current constitution, which critics say gives too much power to the military and court officials.
Kurdish activists in Turkey's southeast, who have waged an armed campaign against the government, called for a boycott of the vote.
The EU's executive European Commission has backed Ankara's attempt to reorganise the judiciary, but accused the government on Tuesday of stifling public debate over the proposals.
The AKP evolved from a series of Islamist parties banned by the courts, but denies having any aims to roll back the republic's traditional secularism.
Polarisation over the referendum reflects Turkey's fractured political landscape, in which a rising middle class of observant Muslims who form the backbone of the AKP have challenged a secular elite which has traditionally held power since Mustafa Kemal Ataturk founded modern Turkey in 1923.
The Konda Institute, which conducted a public survey before voting began, revealed that reforms, including controversial changes to the judiciary, would garner support from 56.8 per cent of voters, although a crucial 17.5 per cent of the electorate remained undecided before the vote.
Tarhan Erdem, head of the Konda Institute, said voting in the referendum would mostly follow party loyalties.
"The lack of a strong party other than AKP is a major shortcoming of Turkish politics. Falling opposition to the reforms is due to a decrease in support for the CHP," he told the Reuters news agency, referring to the opposition Republican People's Party.
Andrew Finkel, a journalist based in Istanbul, agreed that it was a tight call.
"Some people would like to see a sort of narrow win for the 'yes'. I think a lot of people see the package as being in Turkey's interest, but are reluctant to give an open endorsement to a government who has been in power for eight years," he told Al Jazeera.
"I think that people have really forgotten the issue of the constitution in the run-up to this referendum debate [...] it has become very much a referendum, not on the constitutional package, but on the government itself."
Source: Al Jazeera and agencies