KIEV - Ukraine was voting Sunday in a presidential election seen as the most important in the country's history as it battles a deadly pro-Russian insurrection in the east.
Thirty-six million people are registered to vote, but separatist rebels have threatened to block polling "by force if necessary" in areas under their control in the industrial regions on the border with Russia.
AFP correspondents said there were few signs of polling stations open in the east, including the main hub of Donetsk where the insurgents declared their own independent state earlier this month in defiance of Kiev.
"Ukraine is now another country so I don't see why we should take part in this election," said one woman in Donetsk city centre who gave her name as Elisabeta.
"It doesn't matter what the result is, it doesn't concern us today." The West regards the vote as a crucial step in preventing Ukraine from disintegrating further after Russia seized the Black Sea peninsula of Crimea in March, and has warned the Kremlin of further sanctions if it disrupts polling.
Ukraine's Prime Minister Arseniy Yatsenyuk had issued an appeal for voters to turn out in force on Sunday to "defend Ukraine" in the face of a crisis that has plunged relations between East-West relations to a post-Cold War low.
"This will be the expression of the will of Ukrainians from the west, east, north and south," he said Saturday.
Correspondents said voters were flocking to the polls in the capital Kiev and the western nationalist bastion of Lviv.
President Vladimir Putin - authorised by parliament to invade Ukraine if necessary to "protect" ethnic Russians - had appeared to make a major concession Friday by saying he was ready to work with the new Kiev team.
'Respect people's choice'
"We understand that the people of Ukraine want their country to emerge from this crisis. We will treat their choice with respect," he said.
Russia also says it has started withdrawing from Ukraine's border around 40,000 soldiers and dozens of tank battalions whose presence had raised deep suspicions about Russia's next move.
Ukraine is mobilising more than 55,000 police and 20,000 volunteers to ensure security for the vote, being overseen by 1,200 international monitors.
The packed field of candidates features clear frontrunner Petro Poroshenko - a chocolate baron and political veteran who sees Ukraine's future anchored to Europe - and 17 far less popular hopefuls that include ex-premier Yulia Tymoshenko.
The election should give the new president and his government a stamp of legitimacy after pro-EU protests forced out Kremlin-backed leader Viktor Yanukovych in February, setting off a chain of events that now threaten the country's unity.
However, opinion polls show self-made 48-year-old billionaire Poroshenko falling just short of the 50-per cent threshold needed to avoid a second round on June 15, and three weeks of further political uncertainty.
Rebels plan rallies
The authorities acknowledge problems staging polling in the steel mill and coal mine-dotted regions of Donetsk and Lugansk, where rebel leaders declared independent republics after hastily-arranged May 11 referendums.
At least 150 people have been killed since the separatists took up arms against Kiev in early April, according to an AFP tally based on UN and Ukrainian government figures.
As well as grappling with the threats to the country's unity, the new president will have to try to repair relations with Ukraine's former masters in Russia while pushing the nation of 46 million people along a westward track.
Ukraine is hoping that up to $27 billion (20 billion euros) in global assistance it won after the old regime's fall may help avert threatened bankruptcy and revive growth in the recession hit country.
But the new leadership will also have to negotiate with Russia over vital supplies of gas, with Moscow threatening to halt shipments if Ukraine does not pay a bill by early June.
Before voting got under way, Interior Minister Arsen Avakov said on his website the election computer system had been the victim of a cyber attack and that counting would have to be done manually - but a spokeswoman later said the website had itself been hacked and the report was not true.
Voting closes at 1700 GMT, with first results expected from 2100 GMT.
The snap ballot was called by Kiev's interim leaders who took power after Yanukovych fled in the bloody climax of months of protests sparked by his rejection of a historic EU alliance.
The charred buildings and flower-heaped barricades still crisscrossing Kiev's Independence Square - also the cradle of the 2004 Orange Revolution that first shook Russia's historic hold on Ukraine - serve as poignant testimony to the more than 100 people killed in the bloody winter days.
"I hope this election will launch a process of change for the better... but I don't expect a magic wand," said Inna, a voter in the eastern city of Kharkiv that remains in Kiev's control.