There are no immediate reports of injuries.
The unrest started after law enforcement agencies moved to clear Baku's Qalaba (Victory) Square of the protesters.
Thousands of opposition supporters demonstrated on the square today to protest the outcome of the 6 November legislative polls.
Baku city authorities had authorized the meeting. However, opposition leaders called upon their supporters to remain on Qalaba Square after the official deadline expired.
The opposition claims that the 6 November was fraudulent and demand that new polls be held.
A photo gallery of the Azerbaijan opposition protests in Baku on November 9, 2005.