While the opposition declared that it was forming its own government, President Kurmanbek Bakiyev left Bishkek in the presidential plane, though it was not clear whether he was leaving the country or heading to another Kyrgyz city. Earlier in the day, the police used live ammunition, tear gas and stun grenades against a crowd of thousands that massed in front of the presidential office in Bishkek, according to witness accounts.
Dinara Saginbayeva, a Kyrgyz health official, said in a telephone interview that at least 41 people had been killed, “but it could end up being much more.” She said more than 350 people had been wounded in Bishkek alone, with scores of others wounded in protests around the country.
Opposition leaders said the toll could be as high as 100 people.
The upheaval raised questions about the future of an important American air base that operates in Kyrgyzstan in support of the NATO mission in nearby Afghanistan. American officials said that as of Wednesday evening the base was functioning normally.
It also posed a potential embarrassment for the Obama administration, which angered the Kyrgyz opposition last summer by courting Mr. Bakiyev in an ultimately successful attempt to reverse his decision to close the base, angering the opposition.
Tensions had been growing in Kyrgyzstan over what human rights groups contended were the increasingly repressive policies of President Bakiyev, but it appeared that the immediate catalyst for the violence was anger over a reported quadrupling in the prices for utilities.
Mr. Bakiyev made no public comment on Wednesday, and an official at the airport in Bishkek said in a telephone interview that Mr. Bakiyev took off from the airport in the early evening. The airport official said Mr. Bakiyev was flying to Osh, a major city in the southern part of the country, but that could not be confirmed.
On Wednesday afternoon, fighting continued in the streets of Bishkek and other provincial centers. Video shot by protesters and uploaded to the Internet showed scenes of people clashing with and in some cases pushing back heavily armed riot police.
Reports from Bishkek said crowds of opposition members had entered government offices as well as those of the national television channels.
Dmitri Kabak, director of a local human rights group in Bishkek, said in a telephone interview that he was monitoring the protest on the central square when riot police officers started shooting. He said he had the sense that the officers had panicked and were not being supervised.
“When people started marching toward the presidential office, snipers on the roof of the office started to open fire, with live bullets,” Mr. Kabak said. “I saw several people who were killed right there on the square.”
The United States Embassy in Bishkek issued a statement saying that it was “deeply concerned about reports of civil disturbances.”
By late evening in Bishkek, it appeared that the opposition had succeeded in taking over the national television channels. In a speech to the nation, an opposition leader, Omurbek Tekebaev, a former speaker of Parliament, demanded that Mr. Bakiyev and the rest of his government resign.
Mr. Tekebaev was arrested earlier in the day along with some other opposition leaders, but later released.
Kyrgyzstan, with five million people in the mountains of Central Asia, is one of the poorest countries of the former Soviet Union, and has long been troubled by political conflict and corruption.
On Wednesday, the Kyrgyz government accused the opposition of provoking violence. “Their goal is to create instability and confrontation in society,” the Kyrgyz Parliament said in a statement.
The government said it would deal severely with the protesters, but they did not appear to be deterred. The first unrest occurred on Tuesday in the provincial center of Talas, when opposition members stormed government offices.
Russia, which also has military facilities in Kyrgyzstan and a close relationship with the government, appealed for calm.
“We believe that it is important that under the circumstances, all current issues should be resolved in a lawful manner,” the Russian Foreign Ministry said.
Mr. Bakiyev easily won another term as president as president last year over Mr. Atambaev in an election that independent monitors said was tainted by massive fraud.
Mr. Bakiyev first took office in 2005 after the Tulip Revolution, the third in what was seen at the time as a series of so-called color revolutions that offered hope of more democratic governments in former Soviet republics.
But since then, he has consolidated power, cracking down on the opposition and independent news outlets.