Soldiers in Uzbekistan have sealed off the eastern town of Andijan, where some 2,000 protesters are gathered following an overnight jailbreak.
Some of those freed from jail are leading the protest, and include 23 local businessmen who were facing trial on charges of Islamic extremism.
Their families say the men are innocent and have been unfairly targeted.
President Islam Karimov reportedly left for Andijan several hours ago but his current whereabouts are unknown.
Earlier, shots were fired into the crowd. Nine people were killed and 34 injured, according to government officials.
Protesters are calling for “justice” and “freedom”.
The BBC’s correspondent in Tashkent, Monica Whitlock, says the unrest feeds on long pent-up anger in Andijan regarding the treatment of prisoners, poverty, unemployment and other social problems.
Overnight, a group of unidentified armed men broke open Andijan jail, freeing everyone inside – perhaps as many as 4,000 inmates, both political prisoners and ordinary criminals.
They poured out into the city, some of them carrying guns.
“The people have risen,” AP news agency quoted Valijon Atakhonjonov, the brother of a defendant in the long-running trial.
Some protesters have occupied the mayor’s office in Andijan, while the majority are in the main square.
Earlier, three snipers were reportedly pulled down from a roof by protesters.
An official in Uzbekistan’s foreign ministry, who described the protesters as “armed criminals”, said negotiations with them were under way.
All foreign news broadcasts, including those of the BBC, have been blocked.
In the capital Tashkent, 300 km away, a man was shot dead outside the Israeli embassy, upon suspicion he was a suicide bomber.
Our correspondent says the incident, while apparently unrelated to the protests, shows how tense the situation has become.
Andijan is one of the main cities in the most politically sensitive part of this country, our correspondent says.
It is the barometer of feeling for a long, densely populated valley called Ferghana with a long tradition of independent thought, and the authoritarian government in Tashkent has always eyed the valley with suspicion, she says.
The government has locked up probably thousands of local young men, many of them prominent members of the community, accusing them of Islamic extremism.
Neighbouring Tajikistan and Kyrgyzstan have shut their borders with Uzbekistan. Protests in Kyrgyzstan in March resulted in the overthrow of its then President, Askar Akayev.