Kyrgyz police opened fire in a bid to control the crowd who were demanding the resignation of President Askar Akayev in the southern town of Dzhalal Abad, opposition activists said.
"They opened fire, but we don't know where they are firing, it is too loud here," Kushtar, a participant in the protest, said by telephone.
"But if they start to fire at people, then we will just crush them."
Protesters have swarmed around government buildings in southern Kyrgyzstan since the opposition was routed in internationally criticised parliamentary elections, and managed to take over administrative buildings on Friday.
"Most likely they fired blank ammunition into the air," a police spokesman in the capital Bishkek said.
Earlier, police stormed past protesters to recapture administrative buildings in southern Kyrgyzstan, after a two-day stand-off with opposition activists demanding the president's resignation.
Police said they had detained some activists and denied opposition allegations that they used weapons and excessive force to regain the two buildings in Osh, the ex-Soviet Central Asian state's second city, and Dzhalal Abad.
Protesters accused the police of
applying heavy-handed tactics
Other regions, including the capital, Bishkek, have seen opposition protests, with some demonstrators electing "people's councils" after parliamentary polls left the opposition with a handful of seats.
Vote monitors from the Organisation of Security and Cooperation in Europe criticised the poll, held in two rounds in February and March - pointing to vote buying, disqualification of opposition candidates, and media manipulation.
"Yes, the police have taken the building. Force was used against some people, if they showed resistance," a spokesman for Osh region's police said in comments echoed by his colleagues in Dzhalal Abad.
"The building was fully freed by morning. The organisers of the illegal demonstrations were detained, and we have detained 15 people for hooliganism," Omurbek Egemberdiyev, head of the police in Dzhalal Abad region, said.
"No weapons were used, and we caused no injuries. On the contrary, they threw stones, and two policeman were injured and sent to hospital."
"No weapons were used, and we caused no injuries. On the contrary, the protesters threw stones, and two policeman were injured and sent to hospital"
head of police in Dzhalal Abad region
Protesters in mountainous Kyrgyzstan have been inspired by the success of the peaceful Orange Revolution in Ukraine last year, and President Askar Akayev has warned that attempts to copy events in Kiev could lead to civil war.
Protests in Bishkek on Saturday were the largest yet, with
about 1500 people taking part.
Akayev is seen as the most liberal of the presidents ruling the five former Soviet republics in Central Asia, and has pledged to obey the law and stand down at the end of his constitutionally final term as leader later this year.
Protesters say they fear he could use his majority of parliamentary seats, two of which are held by his children, to change the law and stand for another term.
The opposition accused police of using excessive force in seizing the administrative buildings in the south, which is ethnically distinct from the north of the country.
"They beat our boys
with truncheons. I
heard cries over the telephone, then the connection was broken"
Kyrgyz opposition youth wing representative
"They beat our boys with truncheons," Azima Rasulova, representative of the opposition's youth wing, said, adding that she had spoken to the protesters during the storming.
"I heard cries over the telephone, then the connection was broken," Rasulova said.
At least six protesters had been seriously beaten and two truckloads taken away by police, she added.