A protester hit a Carabinieri police vehicle during a demonstration by the 'Indignant' group in Rome October 15, 2011. [Photo/Agencies]

Hundreds broke through a police cordon around the parliament in Lisbon to occupy its broad marble staircase.

"This debt is not ours!" and "IMF, get out of here now!," demonstrators chanted. Banners read: "We are not merchandise in bankers' hands!" or "No more rescue loans for banks!"

Around 4,000 Greeks with banners bearing slogans like "Greece is not for sale" staged an anti-austerity rally in Athens' Syntagma Square, the scene of violent clashes between riot police and stone-throwing youths in June.

Many were furious at how austerity imposed by the government to reduce debt incurred by profligate spending and corruption had undermined the lives of ordinary Greeks.

"They have ruined our world, everything that people have conquered," said Maria Kolozi, 56, a school teacher.

In Paris, around 1,000 protesters rallied in front of city hall, coinciding with the G20 finance chiefs' meeting, after coming in from the working class neighborhood of Belleville where drummers, trumpeters and a tuba revved up the crowd.

"This is potentially the start of a strong movement," said Olivier Milleron, a doctor whose group of trumpeters played the classic American folk song "This land is your land."