Kyrgyz riot police have used tear gas to break up clashes that broke out between supporters and opponents of President Kurmanbek Bakiyev.
Opposition MPs tried to change the constitution
The violence is the first in six days of protests by opposition supporters calling for the president to resign.
Overnight, opposition MPs held an emergency session in parliament to try to pass a new constitution to curb the president's powers.
The government called the move an "open attempt at seizing power".
Several people were injured in the clashes that broke out in the centre of Bishkek. Russian media reported four people had suffered gunshot wounds.
The fighting broke out as thousands of opposition supporters continued their protest close to government buildings, while a pro-government rally of several hundred got under way nearby.
Hundreds of police - some armed and others in full riot gear - encircled the centre of the city where the two demonstrations were taking place, the BBC's Natalia Anteleva reports.
They fired warning shots and used tear gas as bottles, sticks and stones were thrown by both sides.
The violence follows an emergency session of parliament called by the opposition, during which they signed a new draft constitution handing some of the president's powers to parliament.
Opposition MPs said 41 of parliament's 75 deputies signed the document, enough for a simple majority.
TULIP REVOLUTION WILTS
March 2005 - Former President Akayev ousted in popular protest
July - Kurmanbek Bakiyev elected President
April 2006 - Thousands protest for end to corruption and crime
November - Opposition calls for constitutional reform and curbing of presidential powers
But it is not clear if the vote would make the document legal, as Kyrgyz law requires any changes to the constitution to have a two-thirds majority.
Constitutional Court Chairwoman Cholpon Bayekova told the Associated Press news agency that a smaller number of MPs could adopt the law as the situation was "extraordinary".
The government in a statement called the meeting "nothing other than an open attempt at seizing power through anti-constitutional means".
And President Bakiyev warned that he could dissolve parliament if the crisis continues.
"I have not set myself the goal of dissolving parliament," he told a news conference.
"But I have such a constitutional right and of course if contradictions between the legislature and the executive continues what will I have left to do? I cannot watch such an orgy."
The opposition accuse President Bakiyev of pushing the country into a political deadlock by failing to agree to democratic reforms he promised when he was elected in March 2005.
Mr Bakiyev has urged patience, saying reforms should not be adopted in an "hour or two". But the opposition says his time has run out.