His two main opponents, President Viktor Yushchenko and former premier Yulia Timoshenko, have renewed their alliance that denied Yanukovych the presidency in 2004 during the ``Orange Revolution'' and fell apart less than a year later.
Yanukovych's Party of the Regions ranked first in the most recent opinion poll ahead of Timoshenko's bloc and Yushchenko's Our Ukraine party.
The prime minister may struggle to build a coalition with his Communist Party allies after Timoshenko and Our Ukraine agreed to try to form an administration led by Timoshenko.
The result ``will not give an answer to who will control the parliament'' at once, said Paul D'Anieri, professor of political science and associate dean of the University of Kansas, in a telephone interview. ``Timoshenko and Yushchenko are on the track of Yanukovych and this gives them good chances to form the government.''
Voting will end at 10 p.m., with first results from exit polls due soon after and the final result tomorrow. At 4 p.m., turnout was 43 percent, according to the Central Election Commission in Kiev.
More than 50 percent of the 37 million registered voters must cast their ballots for the elections to be valid and a party must win more than 3 percent of the vote to enter the parliament.
Yushchenko's accord with Timoshenko restores the alliance that swept to power in the 2004 Orange Revolution, which was triggered by a rigged presidential election in which Yanukovych, backed by Russian President Vladimir Putin, claimed victory.
The Orange allies, who aim to move closer to the European Union and NATO, fell out during Timoshenko's premiership, allowing Yanukovych to win elections last year and become prime minister.
Our Ukraine was third in the last opinion poll before the elections, with the backing of 13.1 percent of voters, according to a Sept. 1-10 survey of 2,004 voters by the Kiev-based Razumkov Center for Economic and Political Studies. Timoshenko's bloc had 23.5 percent support and Regions 33.9 percent.
Timoshenko and Yushchenko were shown embracing on television on Sept. 27, signaling their accord was restored. The reconstituted Orange bloc may gain enough seats to form a government because of rising support for Timoshenko, analysts said.
To stay in power, Yanukovych's party may have to continue its links with the Communist Party, which is supported by 5 percent of voters, according to the poll. Other smaller parties may garner enough seats to hold the balance of power. They haven't said which coalition they'll support.
``I am sure that we will win and form a coalition,'' Yanukovych said today, according to a statement on his Web site. ``The results of the elections will be not cheated and we will not have early elections in Ukraine in future.''
The Organization for Security and Co-operation in Europe, the main human rights watchdog, has deployed 710 election monitors across the country, said Urdur Gunnarsdottir, spokeswoman for the OSCE's Office for Democratic Institutions and Human Rights. The OSCE has expressed concern about possible irregularities, she said.
``There has been a lot of discussion and complaints about voter lists,'' said Gunnarsdottir, adding that the complaints include suggestions lists are inaccurate and people living abroad may be registered to vote.
After casting his ballot this morning, Yushchenko said in comments broadcast on TV that ``today's elections will be democratic, no one will dare to falsify them. The people's choice will bring stability and economic prosperity to the country. Please, come and vote.''
Kiev's main Independence Square, where hundreds of thousands of Yushchenko supporters gathered to play out the revolution three years ago, was quiet today and filled only with families enjoying the sunshine.
There was no sign of an extra police presence or followers of any of the main parties in the city center.