"I want Ukrainians to know that we are here, all of these people are with them, and glory to Ukraine," said one participant who did not give their name.
"I think that Vladimir Putin is a murderer," said another participant Nina Zvezdina. "So, I am here and I am gonna stay here, support Ukraine and Georgia."
Putin launched what he called a special military operation before dawn on Thursday, ignoring Western warnings and saying the "neo-Nazis" ruling Ukraine threatened Russia's security.
Russia's assault is the biggest on a European state since World War Two and threatens to upend the continent's post-Cold War order.
In 2008 Georgia fought a war with Russia over South Ossetia and Abkhazia. After it ended, Moscow recognized both regions as independent countries.
The Kremlin said it launched its offensive in 2008 to stop a Georgian bid to seize back two pro-Russian Georgian territories that sought to break with Tbilisi.
