Ukrainians are voting in presidential elections that polls show may go to a runoff in June. The vote is seen as the most important since Ukraine's independence in 1991, and crucial to the country's survival after months of turmoil which began when street protests forced out the Kremlin-backed regime in February.

Tensions remain high in the east, following more deadly clashes last week between pro-Russian separatists and government troops. Armed gunmen were able to block voting in the Russian-speaking provinces Donetsk and Luhansk.

Of Ukraine's 36 million voters, around one-seventh live in regions most affected by the insurgent activity. Five million people could be blocked from taking part in Sunday's vote, but despite this, polling shows a heavy turnout elsewhere.

"Chocolate King" in the lead

Billionaire confectionary magnate Petro Poroshenko leads opinion polls, with many wondering if he can take more than 50 per cent to win outright in one round. He has a near 30-point lead over his closest rival, former prime minister Yulia Tymoshenko.

The 48-year-old strongly supported the protests against ousted president Viktor Yanukovych.

Ukrainian interim Prime Minister Arseniy Yatsenyuk has appealed for people to turn out and "defend Ukraine".

"This will be the expression of the will of Ukrainians from the west, east, north and south," Yatsenyuk said on Saturday.

"I want to assure our fellow countrymen in the Donetsk and Luhansk regions who will be prevented from coming to their polling stations by the war unleashed against Ukraine, that the bandits have little time left to terrorize your regions," he said.

Tight security

More than 75,000 police and volunteers will try to ensure voting is secure, alongside 1200 international observers who will monitor the poll. Officials say many polling stations in Ukraine's Russian speaking regions will not open over fears of attacks.

The absence of a significant part of the electorate and the Russian-annexed Crimea may tarnish any result and leave the Kremlin questioning the vote's legitimacy.

Voting began at 8 a.m. (0500 UTC) and ends 12 hours later, with exit polling expected around that time. International monitors will issue their verdict on the process on Monday.

Merkel and Hollande speak with Putin

On Saturday, the leaders of Germany and France telephoned the Russian president over their concerns on Ukraine. Statements issued from the three leaders afterwards indicated that all agreed Ukraine's voting on Sunday should proceed as peacefully as possible.

The Kremlin - which Germany, France and other Western nations have accused of fanning the rebellion in Ukraine's east - said the three leaders expressed "an interest in seeing that the presidential election in Ukraine was held in a peaceful and calm atmosphere."

On Friday, Putin promised to recognize the outcome of Sunday's Ukraine vote. He has brushed off threats from Washington and Europe of more sanctions if Moscow disrupts the election.

jr/mr (Reuters, AFP, AP)