The demonstrations were called for late afternoon, some still taking place around 9:30 pm, and filled the streets and squares of cities such as Madrid, Barcelona, Seville, Bilbao, Granada, Valencia, Santiago de Compostela, and Vigo, among others.

The largest demonstration was in Barcelona, where 15,000 people took to the streets, according to data from the city hall of Spain's second-largest city.

In Barcelona, where the Sumud Global Flotilla departed at the end of August, a group of protesters blocked a road leading into and out of the city.

Another group is holding court in a square near the port of Barcelona, where they plan to set up a camp in solidarity with Gaza and make this location a continuous protest site. In Madrid, the protest began with a gathering in front of the Ministry of Foreign Affairs, followed by a march of 10,000 people, according to authorities, toward the Spanish parliament, which continued after 9 pm.

"This is not a war, it is a genocide," protesters shouted in the Spanish capital, referring to Israel's military offensive in the Palestinian territory of the Gaza Strip.

Before demonstrations called for the end of the day in several Spanish cities, around 20,000 high school students also took to the streets in 40 cities across the country throughout the day in solidarity with Gaza and the Sumud Global Flotilla.

The demonstrations, called by the national association Student Union, were also larger in Barcelona (6,500 people, according to local police) and Madrid (4,000).