A leading opponent of the Akayev regime, Felix Kulov, was freed from prison and said Akayev had signed a letter of resignation, the ITAR-Tass news agency reported. Kulov said the opposition would guarantee Akayev's security "because there must be a peaceful transfer of power".
Kurmanbek Bakiyev, one of two key opposition leaders, said on opposition-controlled state television that "Akayev is no longer on the territory of Kyrgyzstan." He also said Prime Minister Nikolai Tanayev had resigned, but that the Security, Interior and Defense Ministries were working with the opposition.
The Interfax news agency, without citing sources, said Akayev had flown to Russia, but it later said he changed course for Kazakhstan and landed there. Earlier, the news agency said Akayev's family had been heading to Kazakhstan.
Members of the upper house of parliament that was in power before February's election met Thursday night to discuss keeping order in the nation and conducting a new presidential vote, perhaps as early as May or June. They elected a former opposition lawmaker, Ishenbai Kadyrbekov, as interim president.
The lower house of parliament also named prominent opposition leader Kurmanbek Bakiyev acting prime minister early Friday, a lawmaker said after the chamber held a closed-door session.
Legislator Karganbek Samakov told reporters that the lawmakers had named Bakiyev to head the interim government and would be choosing acting ministers later Friday, when they reconvene. He made no other statements, and Bakiyev left parliament without commenting.
Under Kyrgyzstan's old governmental system, most power rested with the president. It was not clear whether duties would be divided similarly under the interim system.
It was also unclear whether the decision was legally binding — in part because of uncertainty over whether Akayev had indeed stepped down.
A member of the upper house of parliament, Temir Sariyev, said "nobody knows what is legitimate right now."
Shortly after the demonstrators streamed into the government headquarters, opposition activist Ulan Shambetov sat in Akayev's chair in celebration, another demonstrator holding a Kyrgyz flag triumphantly behind him.
"It's not the opposition that has seized power, it's the people who have taken power. The people. They have been fighting for so long against corruption, against that (Akayev) family," Shambetov said.
In Washington, Secretary of State Condoleezza Rice said the upheaval in Kyrgyzstan could wind up a democratic success story if political change occurs without violence.
"This is a process that's just beginning. We know where we want to go," Rice said.
"If we can take events on the ground ... encourage the various parties in Kyrgyzstan to move into a process that will then lead to the election of a government and move this process of democracy forward, it will have been a very good thing," Rice said after a meeting with Greek Foreign Minister Petros Molyviatis.
Rice said she discussed Kyrgyzstan with President Bush on Thursday. The Organization for Cooperation and Security in Europe is leading international efforts to promote a peaceful outcome, she said.
"Our desire is for a process that will lead to a stable outcome in which elections can be held and where this can move forward," Rice said. "Obviously, everyone should put aside violence. There is no place for violence in a process of this kind."
The United States would not confirm reports that Kyrgyzstan's president has fled the country following street demonstrations, and Defense Secretary Donald H. Rumsfeld cast doubt on those reports.
"The intelligence reports do not verify what you cited," Rumsfeld answered when asked directly about reports that President Askar Akayev had fled.
Rumsfeld, traveling in Central America, also said he did not believe that U.S. forces in Kyrgyzstan would be harmed by the turmoil. There are roughly 1,000 U.S. troops at Manas air base outside of Bishkek.
Kyrgyz politics depends as much on clan ties as on ideology, and opposition figures have no unified program beyond calls for more democracy, an end to poverty and corruption, and a desire to oust Akayev, who has been in power in the former Soviet republic since independence was declared in 1991.
There is no sign that the opposition would change Kyrgyzstan's policy toward Russia or the West — and unlike in successful recent anti-government protests in Georgia and Ukraine, foreign policy has not been an issue. But any change would have impact, since both the United States and Russia have cooperated with Akayev and have military bases near Bishkek.
There is also no sign the opposition would be more amenable to Islamic fundamentalist influence than Akayev's government has been.
The takeover of government buildings in Bishkek followed similar seizures by opposition activists in southern Kyrgyzstan, including the second-largest city, Osh. Those protests began even before the first round of parliamentary elections on Feb. 27 and swelled after March 13 run-offs that the opposition said were seriously flawed. U.S. and European officials concurred.
Akayev's reported resignation and flight came hours after hundreds of opposition supporters, protesting alleged fraud in parliamentary elections earlier this month, stormed government headquarters in Bishkek.
The Supreme Court later ruled the parliamentary elections invalid, said former parliament speaker Abdygany Erkebayev.
Celebration mixed with chaos Thursday night as thousands stayed on the main square outside the presidential headquarters. An elderly man and woman in a clearing in the crowd danced to imaginary music as a man pretended to beat drums.
After dark, a large store on the main street, Beta, was among a number looted, with a crowd of mostly wild young men carting out everything from mattresses, coat hangars and mirrors to crates of food, juice and cookies.
As midnight approached, looters streamed down a side street carrying bulging bags and parcels that they appeared to have stolen from stores. One teenager held three identical shoeboxes, while a young man weaving as if drunk carried a stack of pink plastic baby bathtubs.
"The most important thing is not to allow revenge and persecution," said Kulov, who had been imprisoned under Akayev on corruption charges he said were politically motivated. "We will try to restore order by the morning. We are trying to do what we can."
Topchubek Turgunaliyev, an activist of the opposition People's Movement of Kyrgyzstan, said new parliamentary elections would be held in the fall.
"We want to preserve the unity of the nation. We are holding talks with law enforcement officials so there is coordination," said Turgunaliyev, whose party is headed by Bakiyev.
Many of the protesters who broke into the government building, whooping and whistling, were young, including members of youth opposition factions that have taken a more confrontational stance against law enforcement officers during the demonstrations.
Thursday's seizure of the government headquarters was the culmination of the first major rally in the Kyrgyz capital since opposition supporters seized control of key cities and towns in the south this week to press demands that the long-serving Akayev step down amid widespread allegations of fraud in this year's parliamentary vote.
"It is a revolution made by the people," Kulov, said on state television, adding, "Tomorrow will come, and we must decide how to live tomorrow."
Kyrgyzstan lacks the rich energy resources or pipeline routes that have made of some of its Central Asian neighbors the focus of struggles by Russia, the United States and China for regional influence. But the former Soviet republic's role as a conduit for drugs and a potential hotbed of Islamic extremism, particularly in the impoverished south, makes it volatile.
Both the United States and Russia — which is part of a six-nation military pact with Kyrgyzstan — maintain military bases near Bishkek, and Moscow said Thursday it had increased security at its facility.
An unknown number of protesters were injured in a clash with men in civilian clothes and blue armbands, who threw stones and brandished truncheons to threaten demonstrators. Vincent Lusser, spokesman for the International Red Cross in Geneva, said staff from the organization had seen "a few dozen wounded" in Bishkek hospitals. Most appeared to have injuries sustained in falls or fist fights, he said.
Many demonstrators wore pink or yellow headbands signifying their loyalty to the opposition — reminiscent of the orange worn by protesters who helped bring in a new, pro-Western president in Ukraine last year.
Akayev, 60, is prohibited from seeking another term, but the opposition has accused him of manipulating the parliamentary vote to gain a compliant legislature that would amend the constitution to allow him to stay in office beyond a presidential election set for October. Akayev has denied that.
He presented himself as a cautious democrat, saying he supported democratic values but that they must be introduced gradually because Kyrgyzstan has not had a long experience with democracy. His opponents claim that was a cover for an intention to establish authoritarian rule. Akayev's last allowable five-year term in office was to expire this year.