An exit poll by Ipsos Global pollster commissioned by the pro-opposition Mtavari TV has shown opposition parties won 61.4 percent of the votes, against 38.6 percent for the ruling party.
Polls have closed in Georgian municipal elections, a day after the dramatic arrest of ex-president Mikheil Saakashvili, who called from custody for the country's "peaceful transition to a genuine democracy".
An exit poll by Ipsos Global pollster commissioned by the pro-opposition Mtavari TV on Saturday showed opposition parties won 61.4 percent of the votes, against 38.6 percent for the ruling party.
A rival exit poll by the local pollster, Gorbi, prepared for the pro-government Imedi TV, showed opposition parties garnering 52.4 percent of the vote with the ruling party on 47.6 percent.
The EU mediated an inter-party agreement in May, under which the ruling party pledged to hold snap parliamentary elections if it wins less than 43 percent of the vote on Saturday.
The detention on Friday of Georgia's foremost opposition figure upon his return from exile raised the stakes in the polls seen as a key test for the increasingly unpopular Georgian Dream ruling party.
READ MORE: Georgia arrests ex-president Saakashvili after return from exile
In comments to AFP through a representative, who visited him in prison on Saturday, Saakashvili said "Georgia needs a peaceful transition towards a genuine democracy where political opponents are not locked up on falsified charges or forced into exile."
"I am not seeking any political office, I am just determined to fight to the end against the oligarchic rule which kills Georgian democracy," he said.
He was referring to the former prime minister Bidzina Ivanishvili, a powerful oligarch and ruling party founder who is widely believed to be calling the shots in Georgia despite holding no political office.
Founder of Georgia's main opposition party, the United National Movement (UNM) and president between 2003-2013, Saakashvili, 53, said on Friday he had secretly returned from Ukraine, where he heads a Ukrainian government agency steering reforms.
READ MORE: Georgian police arrest top opposition leader, deepening political crisis
Both camps claim victory
The flamboyant pro-Western reformer, who in 2003 led the peaceful "Rose Revolution" that ousted Communist-era elites, and still commands a fiercely loyal following, was detained shortly afterwards over a 2018 conviction in absentia on abuse of office charges.
He has denied any wrongdoing, denounced his sentence of six years in jail as politically motivated, and following his arrest went on hunger strike, Georgia's rights ombudsperson said.
Prime Minister Irakli Garibashvili defended the decision to detain Saakashvili, saying "we are all equal before the law, political leaders and ordinary citizens."
Both the ruling party and the opposition each said they were set to win the elections after polls closed at 1600 GMT.
"I congratulate our party and the whole country," Garibashvili told supporters. "Time has come to end political polarisation in Georgia."
The UNM chairman, Nika Melia, said: "The opposition is winning. We should defend every single vote, so that Georgian Dream can't manipulate elections results."
Earlier on Saturday, he accused the government of "voter intimidation and vote buying", but the ruling party said in a statement the vote is "being held at highest democratic standards".
Turnout stood at 41 percent by 5pm (1300 GMT), said the central election commission, which is expected to start releasing vote results on Sunday.
READ MORE: Georgia opposition boycott election runoffs
'They must go'
Standing in a long queue of voters outside a polling station in central Tbilisi on Saturday afternoon, 27-year-old painter Luka Samushia, said: "It will be difficult for the government to falsify vote results if the turnout is high.
"They must go, they can't jail Saakashvili and remain in power," he added.
The municipal elections were being watched inside and outside Georgia for signs of the ruling party backsliding on democracy.
Critics have accused Georgian Dream – in power since 2012 – of using criminal prosecutions to punish political opponents and journalists. Interpol turned down requests from Tbilisi to issue a red notice against Saakashvili.
Opposition parties decried widespread fraud and refused to take their seats after last October's parliamentary elections, which Georgian Dream won narrowly.
They have since staged mass protests, demanding snap polls.
The ruling party withdrew from the pact in July, but the European Union and the United States urged the EU-aspirant country's government to implement the agreement that envisages sweeping political and judiciary reforms.
Saakashvili insists the deal remains in place, saying the upcoming elections "are a referendum on Ivanishvili's removal from power".
With concerns mounting in the West over the ruling party's democratic credentials, the United States has hinted at possible sanctions against Georgian Dream officials.
READ MORE: Georgia's ruling party claims election victory, opposition cries foul