Ukraine opposition leader Viktor Yushchenko has claimed victory in the re-run of the presidential election, as early results indicate a clear lead.
Mr Yushchenko hailed the start of a "new political year"
With 80% of the votes counted, Mr Yushchenko is 14 points ahead of Prime Minister Viktor Yanukovych.
He hailed a new era in Ukraine but the results could be challenged.
The original vote, won by Mr Yanukovych last month, was annulled due to fraud. Sunday's re-run was monitored by 12,000 international observers.
RESULTS SO FAR
Source: Ukraine Central Election Commission, with 80% of votes counted
At about 0000 GMT, Mr Yushchenko declared: "I want to say this is a victory of the Ukrainian people, the Ukrainian nation. We were independent for 14 years, today we became free.
"Today, in Ukraine, a new political year has begun. This is the beginning of a new epoch, the beginning of a new great democracy."
Shortly afterwards he addressed tens of thousands of jubilant opposition supporters in Kiev's central Independence Square, thanking them for their support and urging them to remain in the square until he was officially declared as the winner.
Yushchenko supporters, in their distinctive orange colours, celebrated the anticipated victory with a concert and a fireworks display.
As polls closed, Mr Yanukovych - who has not conceded defeat - vowed to lead "a strong opposition" if he lost, saying it would be "senseless" to negotiate with his rival.
An aide, Nestor Shufrich, later told reporters it appeared likely the numbers would put Mr Yanukovych in second place.
But he added: "We don't admit defeat. If the results of the vote are contested in certain precincts, the outcome of the election could be different."
The Ukrainian Committee of Voters, a voters' rights organisation, said in an initial statement it could see no grounds to talk about mass irregularities in Sunday's re-run.
Many Ukrainians, going back to the polls for the third time in less than two months, said they wanted to put an end to the country's bitter political crisis .
THIRD TIME AROUND
Repeat of 21 November run-off after cancellation of result
Fourth presidential election since independence in 1991
36 million voters; 12,000 foreign election observers
Public support for Mr Yanukovych - once seen as the favourite of the Ukrainian establishment and neighbouring Russia - has been strong in the industrialised east and the south of the country.
Russian President Vladimir Putin has said he will accept, and work with, whoever wins.
Outgoing President Leonid Kuchma suggested the loser should concede within two days.
"Dear God, let this be the final vote. I'm sure it will be," he said.
Mr Kuchma backed Mr Yanukovych in the earlier vote - but the prime minister had recently attacked the president, presenting himself as an anti-establishment candidate.
Allegations of vote-rigging in the original ballot were just part of a campaign characterised by alleged dirty tricks.
Doctors recently confirmed that Mr Yushchenko, who developed a disfiguring skin condition in September, had been poisoned with dioxin.
The opposition leader has suggested he was poisoned at a dinner with heads of the Ukrainian security service (SBU) - an allegation denied by the SBU.