Opposition leaders denied responsibility for events taking place on the central square in the capital saying the crowd had refused to obey their orders.
Additional police reinforcements are arriving at Bishkek's central square as protesters were reported to have thrown stones at the police.
The country's parliament speaker said earlier Thursday mass protest rallies in the Kyrgyz capital Bishkek have succeeded in securing several opposition demands.
"Opposition rallies have not been in vain. Parliament has agreed to negotiate. Some results have been achieved," said Marat Sultanov during a Bishkek-Moscow satellite hookup organized by RIA Novosti.
He said parliament may not be considering opposition demands concerning reform of the country's Constitution, because by law legislation can only be initiated by at least 300,000 voters, a majority of MPs (at least 38) or the president.
"There are no other legal mechanisms," he said, adding that the opposition has now effectively withdrawn its draft Constitution.
He said the situation in the country is being influenced by certain external forces, specifically the EU, U.S., Kazakhstan, China and Russia.
Protesters have been rallying in central Bishkek for nine days demanding that the new Constitution reducing presidential powers be adopted and early elections called. The protests were organized by the United Front of Kyrgyzstan, a major opposition movement.
President Kurmanbek Bakiyev signed a draft Constitution, the third in the past six months, April 10, and handed it over to the legislature. However, lawmakers have resisted debate, citing street pressure. A working group led by Prime Minister Almaz Atambayev, a former liberal opposition leader, drafted the document.
The radical opposition, led by former Prime Minister and former presidential ally Felix Kulov, has also drawn up its own variant, and will soon submit it to legislature.
Kulov, who came to power on the back of a violent uprising in 2005 together with the president, said some members of parliament were deliberately delaying consideration of the draft law, adding that pro-presidential deputies could also try to "block the election of Constitutional Court judges."
The Constitutional Court has been unable to make a quorum for the past six months. Under local law, parliament cannot start debating constitutional changes until the Constitutional Court reaches a conclusion.
In November, the power struggle in the impoverished republic ended up with a new Constitution that was signed under pressure from the liberal opposition movement For Reforms, led by the current premier at the time.
The law curtailed presidential powers and almost turned the country into a parliamentary republic. But deputies passed a new Constitution December 30 that restored the president's authority after Bakiyev threatened to dissolve parliament.
