Thousands of protesters were today gathering in Tbilisi to demonstrate against the Georgian president, Mikheil Saakashvili.
Demonstrators in what will be the largest anti-government protest in Georgia since last summer's disastrous war with Russia are demanding Saakashvili's immediate resignation.
They have pledged to continue staging street protests until he quits.
Opposition politicians accuse Saakashvili of presiding over an increasingly authoritarian and repressive regime.
They have also attacked him over his handling of the conflict with Russia last August, sparked when he attempted to recapture the breakaway region of South Ossetia.
The move provoked a punitive invasion by Moscow and the loss of additional territory previously controlled by Georgia.
Opposition leaders predicted 150,000 people would attend today's rally outside the parliament building in the Georgian capital.
Hundreds of riot police and fire engines surrounded the building overnight. The government and opposition have both called for a peaceful protest.
Opposition to Saakashvili has grown steadily since the 2003 Rose Revolution in the former Soviet republic swept him to power.
In November 2007, the president used riot police and tear gas to disperse an anti-government rally, prompting criticism from the US, Georgia's key western backer, and the EU.
The Georgian opposition, however, has its own failings. It has frequently been weak and divided and has so far been unable to capitalise on Saakashvili's alleged blunders.
It also has no constitutional way of removing the president, who was re-elected for a second term in 2008 and is not obliged to step down from office until 2013.
"I'm pretty sure Saakashvili won't resign," Zaza Gachechiladze, a Georgian analyst and the editor in chief of Georgia's The Messenger newspaper said today.
"Unfortunately, he doesn't recognise last year's war as a defeat," he added. "He keeps stubbornly saying he is going to stay.
"There is no mechanism whatever to force him to resign. Historically, however, he is finished.
"If he doesn't go today he has to go in three or six months. He will not survive until the end of his official term. He now has very little support in the country."
Some Georgians are tired of political bickering in the capital and sympathetic to government calls for stability amid the global crisis, which the International Monetary Fund has warned will have a deeper impact in Georgia than first predicted.
Saakashvili's youthful, mainly western-educated team came to power praised by the former US president George Bush as a "beacon of liberty".
But the light has faded, and diplomats say Barack Obama's administration will be less forgiving.
Today the opposition leader, Nino Burjanadze, said police had detained 60 of her supporters.
Last month, the authorities said they had uncovered a plot to overthrow the government.
Today's rally has been timed to coincide with the 20th anniversary of a deadly crackdown by Soviet troops against Georgian protesters demanding independence for the republic of 4.5 million people.
Hundreds of Georgians laid red roses at the steps of the parliament in memory of the victims.