The protests are taking place in front of the Georgian parliament where about 20 tents have been set up. The protesters are demanding a repeat of the country's presidential elections, which returned President Mikheil Saakashvili to office.
Western monitors earlier said Georgia's elections were generally fair, although they admitted there had been a number of violations.
The U.S.-educated Saakashvili has moved to integrate the country into the European Union and NATO since he came to power in 2004, but has been criticized recently for authoritarianism, corruption and economic failure.
The protesters are also demanding the resignation of Parliament Speaker Nino Burdzhanadze and the release of all persons detained during the opposition rally in central Tbilisi in November 2007, which turned into clashes between protesters and police.
