Romanians have gone to the polls to decide whether to impeach their president, Traian Basescu, bringing to a head weeks of political warring that has mired the young democracy.
Polling stations opened at 04:00 GMT on Sunday. Around 18.3 million people are eligible to vote, including large diasporas in Spain and Italy.
The opening hours have been extended and a number of additional polling stations have been set up along the Black Sea coast to facilitate voting for holidaymakers and rural populations in a country where voter fatigue is high.
Opinion polls show two-thirds of Romanians are expected to vote in favour of impeaching Basescu, once one of the country's most popular politicians whose ratings plummeted amid austerity cuts in 2010.
| Romania's president faces impeachment vote
In case turnout is lower than 50 per cent, the referendum will be declared invalid and Basescu, suspended by parliament earlier this month, will be reinstated and continue his mandate, which ends in 2014.
Romania has been gripped by a bitter conflict between the conservative president and the Social-Liberal Union (USL) of Prime Minister Victor Ponta, which took power in May and quickly moved to oust Basescu.
"Go vote, impeach him", read banners put up around Bucharest ahead of the vote by the USL, which has appealed for high voter turnout.
"We must not forget that we cannot install solid and lasting democracy without the votes of as many people as possible," said interim president Crin Antonescu on Friday.
Basescu and opposition Liberal Democrats have meanwhile called on voters to boycott a referendum they say would "legitimise a coup". They claim the ruling coalition plans to rig the vote.
Basescu said last week that he was willing "to govern with the current majority to ensure the country's stability".
If the yes vote triumphs, and Basescu is permanently removed from power, Romania will have to organise a fresh presidential election.
The referendum comes after weeks of contentious moves by the government to manipulate Romania's political institutions, which led to sharp warnings from Brussels and the United States that democracy was being eroded.
Ponta's government removed opposition parliamentary speakers, sacked an ombudsman and clipped the powers of the constitutional court.
The European Commission said the dramas "raise serious doubts" about Romania's understanding of the rule of law but nevertheless praised efforts to fight graft by the anti-corruption prosecutor's office and other institutions.
Last week analysts said civil society groups had been forgotten in the political fray and needed to be involved to help get the derailed political process back on track.