Tens of thousands of people are marching through Madrid's streets in a show of strength by Spain's fledgling radical leftist party Podemos (We Can) which hopes to emulate the success of Greece's Syriza party in elections later this year.

Supporters from across Spain converged onto Cibeles fountain Saturday before packing the avenue leading to Puerta del Sol square.

Podemos aims to shatter the country's predominantly two-party system and the "March for Change" gathered crowds in the same place where sit-in protests against political and financial corruption laid the party's foundations in 2011.

The Spanish party's meteoric rise is also greatly due to the charisma its leader, Pablo Iglesias, a pony-tailed 36-year-old political science professor who has won followers with his determined arguments which, so far, are light on detail.