Georgian President Mikhail Saakashvili has said he is confident of victory in the country's snap election after exit polls gave him a commanding lead.
Mr Saakashvili called the election after opposition protests
The polls suggest he won 53.7% of the vote, which if confirmed by official results would give him an outright win.
But the opposition said there were serious violations and called its supporters to hold a street protest.
The vote is seen as a democratic test for the ex-USSR state after recent opposition protests were suppressed.
The BBC's Matthew Collin in Tbilisi says there has been a mood of celebration around Mr Saakashvili's campaign headquarters, with people waving flags and cars tooting their horns.
But no official results have yet been published and Mr Saakashvili has not claimed victory.
He said he would wait for the final results but was confident of victory without a run-off against his nearest rival.
Analysts are urging caution, as 20% of respondents in the exit poll refused to say who they had voted for, and opposition denounced the survey as a "big lie".
Opposition candidate Levan Gachechiladze, who the pollsters say won 28% of the vote, has accused the government of trying to rig the election.
He said after voting that his supporters were recording numerous violations around the country, and urged them to take to the streets for a mass protest on Sunday afternoon.
The authorities have denied allegations of fraud, and acting President Nino Burjanadze told the BBC that the elections had been "free, fair and democratic".
But our correspondent says that after a bitter and divisive election the dispute seems certain to continue.
Mr Saakashvili called the election after huge opposition protests were suppressed in November, in an attempt to prove his democratic credentials.
Along with the presidential election, Georgians are being asked to vote on whether they should have a parliamentary election in the coming months, and whether the country should join Nato.
Hundreds of foreign observers have been monitoring the ballot.
Mr Saakashvili, a US-educated lawyer, came to power after street protests in 2003, dubbed the Rose Revolution.
His term as president has seen Georgia strengthen its ties with Nato and the European Union.
But relations with Moscow have soured and Georgia's economy has been badly hit by a Russian ban on Georgian goods.