A week before Scotland votes on whether to break away from the United Kingdom, Catalan separatists in north-eastern Spain hope at least one million people will take to the streets in Barcelona and across Catalonia to demand a secession vote.
The central government in Madrid insists that would be illegal.
Several hours before protests began, Catalonia regional leader Artur Mas said today his government is not wavering from plans to hold a secession referendum on November 9 even though experts say such an attempt is sure to be blocked by Spain's Constitutional Court.
Polls suggesting Scotland's Yes independence camp could win their September 18 vote have energised Catalan separatists.
It is also being watched closely by Corsicans who want to break away from France and Flemish speakers in Belgium demanding more autonomy, independence or union with the Netherlands.