Opposition leader Viktor Yushchenko has won the re-run of Ukraine's troubled presidential election by a clear margin, election officials say.
Mr Yushchenko thanked his supporters, who endured bitter cold
With more than 98% of votes counted, the pro-Western leader is eight points ahead of Prime Minister Viktor Yanukovych following Sunday's vote.
International observers from the OSCE monitoring watchdog said the re-run was much fairer than the earlier rounds.
The original vote, won by Mr Yanukovych last month, was annulled due to fraud.
"The Ukrainian people have won," Mr Yushchenko told a jubilant crowd waving orange flags in central Kiev.
But a top Yanukovych ally, Nestor Shufrych, complained of multiple voting and violations in voter lists and warned that "we will appeal against the falsification of the vote".
Mr Yanukovych, who favours closer ties with Russia, has strong support in Ukraine's industrial east.
Sunday's re-run was monitored by 12,000 international observers.
"The Ukrainian elections have moved substantially closer to meet OSCE standards," said Bruce George, the head of an Organisation for Security and Co-operation in Europe (OSCE) monitoring mission.
"The people of this great country made a great step forwards to free and fair elections by electing the next president of Ukraine," he told a news conference.
Mr Yushchenko declared victory at about 0000 GMT, while the counting was still in its early stages.
"This is a victory of the Ukrainian people, the Ukrainian nation," he said. "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."
Mr Yushchenko then addressed tens of thousands of his 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. They have kept up huge rallies in the capital for weeks, despite sub-zero temperatures.
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
As polls closed, Mr Yanukovych - who has not admitted defeat - vowed to lead "a strong opposition" if he lost, saying it would be "senseless" to negotiate with his rival.
Many Ukrainians, going back to the polls for the third time in less than two months, said they wanted to end the country's bitter political crisis.
In the earlier rounds Mr Yanukovych was backed by outgoing President Leonid Kuchma and Russian President Vladimir Putin.
But last week Mr Putin said he would accept, and work with, whoever won.
And President 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 Yanukovych 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 marred 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.