AFP's Matthew Siegel at Bishkek protests: "People said that they'd been shot"
At least four people have been killed in clashes between police and protesters in Kyrgyzstan's capital, Bishkek, witnesses and medics say.
There are reports that police fired live rounds at the demonstrators after failing to disperse them with tear gas and stun grenades.
Protesters in several parts of the country are calling for the president to resign over rising fuel prices.
Russia and the US, which have military bases in Kyrgyzstan, appealed for calm.
The clashes in Bishkek come a day after thousands of people stormed government offices in the north-western town of Talas.
Government offices in another town, Naryn, have also been seized by opposition supporters.
President Kurmanbek Bakiyev has declared a state of emergency and imposed customs in Bishkek, Talas and Naryn.
Witnesses said at least four bodies were on the ground in the square outside the president's office and a medical official told Reuters news agency that several people had been killed and dozens injured, mostly from firearms.
AT THE SCENE
Rayhan Demytrie, BBC News, Bishkek
We've been to the square where the demonstrations were taking place - the situation is very chaotic.
There are thousands of people there, mainly young men, and lots of them have arrived from different parts of Kyrgyzstan.
They are very angry and it was very noisy, the police were firing stun grenades and also live rounds. We saw people who had been shot - one man walked past me, he had been shot in the hand.
We seemed to be the only camera there - and the protesters wanted us to see the people who had been killed. We saw at least one dead man.
All this has angered the protesters even further - they say they won't go anywhere and were shouting "the president must go".
The protesters in Bishkek appeared to be leaderless, says the BBC's Rayhan Demytrie in the capital, after a number of opposition heads were arrested overnight.
Earlier, police had used tear gas and stun grenades to break up crowds outside an opposition headquarters but the protesters overcame the police and marched to the presidential offices in the city centre.
Police cars have been overturned and set alight and officers attacked by the crowd, some of whom are reported to be armed.
The unrest began on Tuesday in Talas, where protesters briefly took the local governor hostage while another group surrounded the local police headquarters.
Angry crowds attacked special forces police with rocks and petrol bombs. They reportedly set fire to portraits of President Bakiyev.
Prime Minister Daniyar Usenov said at least 85 people were injured in the unrest - most of the injured were reported to be police officers.
Protests spread on Wednesday to Bishkek and Naryn.
Thousands of people occupied a government building in Naryn and have installed what they are calling a "people's governor".
The protests have been touched off by rising fuel prices, but the opposition has also accused President Bakiyev of economic mismanagement and failing to tackle corruption.
One of the poorest of the former Soviet states
Hosts both US and Russian military air bases
Population mostly Kyrgyz but 15% are Uzbek and a significant number of Russians live in the north and around the capital
Kurmanbek Bakiyev has been president since the Tulip Revolution of 2005, which overthrew the government of Askar Akayev
Mr Bakiyev vowed to restore stability but has been accused of failing to tackle corruption
Opponents also complain he has installed relatives in key government posts
Domestic media have come under increasing pressure from the government in recent months
The most popular opposition leader, Almazbek Atambayev, and several other politicians have been arrested and journalists attacked, adding to the tensions in the country, says our correspondent.
In a statement, the US embassy in Bishkek said it would call on "all parties to show respect for the rule of law and call on both the demonstrators and the government to engage in talks to resolve differences in a peaceful, orderly and legal manner".
The US base in Manas, near Bishkek, is a key resupply hub for the operations in Afghanistan.
Russia's Foreign Minister Grigory Karasin has urged the authorities not to use force against demonstrators, the Interfax news agency reported.
In recent weeks, the authorities have clamped down on independent media, and several internet news sources are still blocked in the country.
PRESIDENT KURMANBEK BAKIYEV
Came to power after "Tulip Revolution" street protests in 2005
His party won every parliamentary seat in 2007 polls - which observers said did not meet international standards
Won re-election again in 2009 - but EU observers again said poll was flawed
Opposition accuses him of a media crackdown, nepotism and corruption
This page is best viewed in an up-to-date web browser with style sheets (CSS) enabled. While you will be able to view the content of this page in your current browser, you will not be able to get the full visual experience. Please consider upgrading your browser software or enabling style sheets (CSS) if you are able to do so.