Hundreds of protesters now apparently control the building, the seat of the Kyrgyz government. They are demanding the resignation of President Askar Akaev.
AP reports that officials could be seen leaving the building, although other reports suggest that some officials are trapped inside. It was not immediately clear where President Akaev was.
Bubukan Dosalieva, RFE/RL's Radio Azattyk correspondent, filed this report shortly after protesters went streaming into the building.
"At 2:55 pm Bishkek time [1055 Prague time], most of the people demonstrating on Alatoo [central square of Bishkek] crossed the metal barriers surrounding the 'White House' and entered the government building. Many citizens forced their way through the police lines at the checkpoint outside the building and went in," Dosalieva said.
Demonstrators also occupied Kyrgyz state television and are broadcasting scenes from the protest.
One of the opposition leaders, former Prime Minister Kurmanbek Bakiev, is pledging to hold fresh elections. He urged law-enforcement forces to join the protests.
Earlier in the day, demonstrators chased away riot police who had ringed the building after a tense standoff that turned violent at times.
RFE/RL correspondent Jean-Christophe Peuch was at the scene. He describes how police first appeared to hold the upper hand -- and then quickly retreated in the face of the protests.
"The police forces, which are probably several hundred, managed to move toward the center of the square and repel the protesters, and it looked like the police forces had the upper hand for about two minutes. And then, after two or three minutes, the protesters managed to repel the police forces, and this is exactly the moment when the clashes broke out," Peuch said.Widespread Protests
The rally today began peacefully, with thousands gathering in the central square to renew calls that Akaev step down.
But the demonstrations turned violent after apparent Akaev supporters clashed with the protesters.
Anti-government demonstrations are continuing in other cities, including Jalal-Abad and Osh in the south, where protesters have occupied local government buildings. Several people were reported injured over the weekend as demonstrators set fire to buildings and a billboard.
The actions are aimed at forcing Akaev from office and overturning the results of recent parliamentary elections that left government-backed parties overwhelmingly in power.
Those elections were criticized by the Organization for Security and Cooperation in Europe and other Western monitors as flawed.
Photo Gallery: How The Protests Unfolded In The South
Analysis: Uneasy Days In Kyrgyzstan
Region Looks On Events With ConcernFor more on the Kyrgyz elections, see RFE/RL's dedicated website Kyrgyzstan Votes 2005