Ukrainians voted on Sunday in the first presidential elections since the 2004 Orange Revolution in a ballot set to determine the ex-Soviet republic's relations with Russia and Europe.
Election campaigning for 18 candidates came to an end on Saturday. Viktor Yanukovych, leader of the opposition Party of Regions, and Prime Minister Yulia Tymoshenko are seen as the main contenders for the top post.
Both Yanukovych and Tymoshenko have pledged to improve ties with Russia, soured over Kiev's NATO bid, gas disputes and the former Soviet republic's support for Georgia in the August 2008 war over South Ossetia.
Yanukovych said he would follow Russia in recognising the former Georgian republics of South Ossetia and Abkhazia if elected. He also criticised attempts to blame Russia for the 1932-33 famine in Ukraine, RIA Novosti reported.
Tymoshenko pledged that she would seek EU membership for the ex-Soviet state if elected president.
"Yanukovych will be ahead probably by 12 per cent. Tymoshenko's team is still confident she can catch up, she can still win, but the gap must be small, less than 10 per cent," Andrew Wilson from the European Council on Foreign Relations said.
If election polls on Sunday show a 15 per cent lead in favour of Yanukovych over Tymoshenko, then she will not have a chance in the run-offs, Wilson said.
He also said that if Tymoshenko loses the first round by 10-15 per cent to Yanukovych, then street protests and legal suits will be brought to the country's Arbitration Court by Tymoshenko.
Wilson believes presidential candidate Serhiy Tyhypko, favoured in third place, could play a "key figure" in a run-off election between Yanukovych and Tymoshenko.
Tyhypko is currently taking votes away from Yanukovych, which Tymoshenko needs to secure her position.
Incumbent President Viktor Yushchenko, who came to power after the 2004 Orange Revolution, which was triggered by allegations of fraud after Yanukovych was declared the winner of later discredited elections, will receive only 1.5 to 3.5 per cent in the first round, ultimately losing the presidential chair, Wilson said.