At least 100,000 Spaniards angered by grim economic prospects and the political handling of the international financial crisis have turned out for street demonstrations in the country's cities, marking the one-year anniversary of a movement that inspired similar pressure groups in other countries.

Tens of thousands of protesters in Madrid flooded into the central Puerta del Sol plaza in the evening and aimed to stay for three days. But authorities warned they wouldn't allow anyone to camp out overnight, and up to 2000 riot police were expected to be on duty.

"I'm here to defend the rights that we're losing and for the young people who have it so tough," 57-year-old middle school teacher Roberto Alonso said. "They're better educated than ever. But they don't have work. They don't have anything. They're behind and they'll stay that way."

At least 20,000 people demonstrated in Barcelona. Marches were also held in Bilbao, Malaga and Seville. Sympathisers held protests in other European cities.