Protesters at rallies across Russia have demanded new parliamentary elections and the resignation of the prime minister Vladimir Putin.
Russian media report that the largest rally, in Moscow, drew more than 50,000 people.
The ABC reports there were also anti-government rallies across the country, from the far east to Siberia, to the European enclave of Kaliningrad.
The opposition and protesters say the parliamentary election on 4 December was rigged in favour of the ruling United Russia party.
This week the government announced a long list of political reforms, but it has refused to re-run the vote.
One of the protest leaders, Alexei Navalny, told the crowd in Moscow that Russians would no longer tolerate corruption and vowed that one million people would attend the next rally to demand new parliamentary elections.
The wave of rallies, taking place 20 years after the fall of the Soviet Union, is the biggest show of public anger since the chaotic 1990s and the first challenge to Mr Putin's12-year domination of Russia, the ABC reports.
As the protests were held, the last Soviet leader, Mikhail Gorbachev, called on Mr Putin to quit, just as he had done when the USSR collapsed.
Mr Gorbachev, 80, who has been critical of the elections and was considering attending, was not able to appear. He passed his greetings to the protesters and in an evening radio interview called on Mr Putin to step down.
