The apparent toppling of the pro-Russian leader looks likely to dramatically alter the future of the former Soviet republic of 46 million people, pulling it closer to Europe and away from Moscow's orbit.
It is also a stark reversal for Russian President Vladimir Putin's dream of recreating as much as possible of the Soviet Union in a new Eurasian Union, in which Moscow had counted on Yanukovich to deliver Ukraine as a central member.
The Ukrainian parliament, which decisively abandoned Yanukovich after loyalists defected, declared the president constitutionally unable to carry out his duties and set an early election for May 25.
Deputies in the assembly stood, applauded and sang the national anthem.
In a television interview shortly beforehand, which the station said was conducted in the eastern city of Kharkiv, Yanukovich said he would not resign or leave the country, and called decisions by parliament "illegal".
"The events witnessed by our country and the whole world are an example of a coup d'etat," he said, comparing it to the rise of the Nazis to power in Germany in the 1930s. He said he had come under fire. "My car was shot at. I am not afraid. I feel sorrow for my country," he told UBR television.
Despite his defiance, the dismantling of his authority seemed all but complete with his cabinet promising a transition to a new government, the police declaring themselves behind the protesters and his jailed arch adversary expected to go free.
Among a series of acts aimed at removing his government, parliament voted to free jailed former prime minister Yulia Tymoshenko. Her daughter said Tymoshenko was already free under Ukrainian law but still in the hospital where she has been held for treatment.
The newly-installed interior minister declared that the police now stood with demonstrators they had fought for days, when central Kiev became a war zone with 77 people killed.
At the president's headquarters, Ostap Kryvdyk, who described himself as a protest commander, said some protesters had entered the offices but there was no looting. "We will guard the building until the next president comes," he told Reuters. "Yanukovich will never be back."
The grounds of Yanukovich's residence outside Kiev were also being guarded by "self-defence" militia of protesters.
"RESPONSIBLE TRANSFER OF POWER"
"The cabinet of ministers and ministry of finance are working normally," the cabinet said in a statement. "The current government will provide a fully responsible transfer of power under the constitution and legislation."
Polish Foreign Minister Radoslaw Sikorski, who had negotiated concessions from Yanukovich with other European foreign ministers in a deal on Friday, tweeted: "No coup in Kiev. Gov. buildings got abandoned. Speaker of Rada (parliament) elected legally."
Military and police leaders said they would not get involved in any internal conflict. The interior ministry responsible for the police said it served "exclusively the Ukrainian people and fully shares their strong desire for speedy change".
"The organs of the Interior Ministry have crossed to the side of the protesters, the side of the people," new Interior Minister Arsen Avakov told Ukraine's Channel 5 TV.
Yanukovich, who enraged much of the population by turning away from the European Union to cultivate closer relations with Russia three months ago, made sweeping concessions in the deal brokered by European diplomats on Friday after days of pitched fighting in Kiev that saw police snipers gun down protesters.
But the deal, which called for early elections by the end of the year, was not enough to satisfy pro-Europe demonstrators on Independence Square, known as the Maidan, or "Euro-Maidan", who want Yanukovich out immediately in the wake of the bloodletting.
On Saturday, the speaker of parliament, a Yanukovich loyalist, resigned and parliament elected Oleksander Turchynov, a close ally of Tymoshenko, as his replacement.
"Today he left the capital," opposition leader Vitaly Klitschko, a retired world heavyweight boxing champion, told an emergency session of parliament about the president.
"Millions of Ukrainians see only one choice - early presidential and parliamentary elections."
Two protesters in helmets stood at the entrance to the president's Kiev office. Asked where state security guards were, one, Mykola Voloshin, said: "I'm the guard now."
POSSIBLE TYMOSHENKO COMEBACK
The release of Tymoshenko, expected soon, would transform Ukraine by giving the opposition a single leader and potential future president, though Klitschko and others also have claims.
She was jailed by a court under Yanukovich over a natural gas deal with Russia she arranged while serving as premier. The EU had long considered her a political prisoner, and her freedom was one of the main demands it had for closer ties with Ukraine during years of negotiations that ended when Yanukovich abruptly turned towards Moscow in November.
"According to Ukrainian law my mum is already a free person," daughter Yevgenia Tymoshenko told reporters, saying she was on her way to meet her mother in Kharkiv where she has been held in hospital under treatment for back pain.
A spokeswoman for Tymoshenko, 53, said that although the moves in parliament already made her a free woman, she had not yet been released or left the secure hospital.
Underscoring Ukraine's regional divisions, leaders of Russian-speaking eastern provinces loyal to Yanukovich voted to challenge anti-Yanukovich steps by the central parliament.
Eastern regional bosses meeting in Kharkiv - the city where Yanukovich had apparently sought refuge - adopted a resolution saying parliament's moves "in such circumstances cause doubts about their ... legitimacy and legality.
"Until the constitutional order and lawfulness are restored ... we have decided to take responsibility for safeguarding the constitutional order, legality, citizens' rights and their security on our territories."
Kharkiv Governor Mikhaylo Dobkin told the meeting: "We're not preparing to break up the country. We want to preserve it."
In Russia, Mikhail Margelov, head of the foreign policy committee of the upper house of parliament, said the Kharkiv meeting proved "that the Maidan and the opposition, let alone the militants, are not the majority of the Ukrainian people."
But the head of the foreign affairs committee in Russia's lower house, Alexei Pushkov, seemed to acknowledge that Yanukovich's rule was finished. "He fled. Security fled. Staff fled," Pushkov said. "A sad end to the president."
With borders drawn up by Bolshevik commissars, Ukraine has faced an identity crisis since independence. It fuses territory integral to Russia since the Middle Ages with former parts of Poland and Austria annexed by the Soviets in the 20th century.
In the country's east, most people speak Russian. In the west, most speak Ukrainian and many despise Moscow.
The past week saw central state authority vanish altogether in the west, where anti-Russian demonstrators seized government buildings and police fled. Deaths in Kiev cost Yanukovich the support of wealthy industrialists who previously backed him.
Putin had offered Kiev $15 billion in aid after Yanukovich spurned an EU trade pact in November for closer ties with Moscow. The fate of those funds is now unclear.
Washington, which shares Europe's aim of luring Ukraine towards the West, took a back seat in talks, its absence noteworthy after a U.S. official was recorded on an unsecured telephone line disparaging EU diplomacy with an expletive. (Additional reporting by Matt Robinson in Kiev, Gabriela Baczynska in Moscow and Marcin Goettig in Warsaw; Writing by Peter Graff; Editing by Mark Heinrich)