"The PDK leads by six percentage points. Our polls sees the PDK gaining 31 per cent while LDK has 25 per cent," Shkelzen Maliqi, head of the Gani Bobi pollsters, said about a survey of more than 2,000 voters who had declared their vote.
The results mean Mr Thaci would next turn to negotiate for backing from smaller parties which have won supporters away from both the PDK and the LDK. The LDK was the main minority coalition partner in the outgoing government.
Both leading parties seek EU and Nato membership for Kosovo, continued privatisation of state enterprises, and talks with Serbia, but have given few concrete details about their programmes to boost one of the poorest economies in Europe.
In the last national election in 2007, the PDK won 34.3 per cent of the vote, the LDK 22.6 per cent.
Turnout was higher than the previous elections, Mr Maliqi said, without giving a precise figure. A higher turnout might reflect eagerness for change that could cut support for the ruling party, analysts say.
Around 2.2 million people live in Kosovo, according to estimates by the statistics office, but the figures are unreliable as the last census was conducted 30 years ago.
Albanians make up an estimated 92 per cent of the population, Serbs 5.3 per cent and other ethnic groups 2.7 per cent.
The European Union and the United States view the snap election as a test of Kosovo's democratic maturity, and a free and fair vote is a condition for eventual membership in the EU.
A Western election observers' mission led by a European Parliament team is to hold a news conference today.
"I consider the voting process a success," said Valdete Daka, the head of the Central Election Commission. "There have been technical hitches that have not hurt the process."
However, ethnic Serbs in the divided town of Mitrovica boycotted the election, showing lingering tensions from Kosovo's breakaway from Serbia. Nine Serb parties ran and their voters elsewhere in Kosovo went out to cast their votes.
"These elections were organised by a state that does not exist for me and this is the reason why I don't vote," said Dragan Vukosavljevic, an ethnic Serb who lives in the northern town of Mitrovica.
Police arrested two people from a group of 40 Kosovo Serbs in northern Kosovo who protested against the presence of mobile voting booths on the back of trucks.
Serbs offered a different picture in Gracanica, a village close to Pristina.The Serb, European Union and US flags -- the latter a target of Serb hate in the past - hung in front of the town hall and the voting station was packed.
"Everything is going well. People are coming to vote; approximately half of them have come," Dejan Velic, 32, an unemployed Serb father of three, said in the afternoon.
Many ethnic Albanians who were interviewed outside polling stations said they hoped for change.
"I would like to see more courageous leaders who keep their word," said Fatime Sheremeti, aged 47.