Votes are being counted through the night in Romania's presidential election as both candidates appear to be neck-and-neck.
Opposition supporters celebrate but both candidates sense victory
Exit polls for Sunday's run-off ballot show both Adrian Nastase and Traian Basescu have an equal number of votes.
Authorities are expected to release initial results on Monday morning.
Ruling party candidate Mr Nastase, who is currently prime minister, won the first round on 28 November, with 41% of the vote compared to Mr Basescu's 34%.
Singing and dancing
The BBC's Nick Thorpe in Bucharest says the apparent tie has been interpreted by opposition supporters as evidence of a significant shift in support towards Mr Basescu, after Mr Nastase's seven-percentage point advantage in the first round.
They have spilled out onto the streets of the capital, clutching orange flags and balloons and singing and dancing.
Exit polls show that the candidates are tied
Mr Basescu, who is mayor of Bucharest, urged them to celebrate peacefully and leave the square until Monday evening.
But hundreds of his supporters remain in University Square.
"If Basescu doesn't win. We will have a second Ukraine. I will stay here until they get rid of Nastase," Dan Jijiev, a 34-year-old engineer told the Associated Press news agency.
Both candidates told supporters they were confident of victory.
Mr Nastase said the official count on Monday would hand him a victory and declared: "I will be a strong president."
Likewise, Mr Basescu said he was also confident he would win.
He said: "I thank the Romanian electorate and I assure them I will be a president for Romania."
The ruling Social Democrats need Mr Nastase to win if they are to hold on to power after no party won a clear majority in parliamentary elections two weeks ago.
The Social Democrats 189 of the 469 seats, while Mr Basescu's Justice and Truth Alliance won 161.
Although presidential powers in Romania are limited, the head of state will play a pivotal role in the hung parliament.
It is up to the president to nominate the next prime minister.
Mr Nastase said he would nominate Foreign Minister Mircea Geoana while Mr Basescu proposed his political running-mate, Calin Tariceanu.
Whoever ends up in charge will face a tough task of speeding up reforms necessary to make true Romania's dream of EU membership, our correspondent says.