The demonstrations were held as a show of support for the arrested former Catalan president Carles Puigdemont.
German police had earlier arrested Puigdemont as he crossed the border with Denmark by car, responding to a European warrant issued by Spain.
Puigdemont had entered Germany from Denmark after leaving Finland on Friday when it appeared police would arrest him there and launch an extradition process requested by Spain.
Puigdemont, who lives in self-imposed exile in Belgium, had been visiting Finland since Thursday for talks with lawmakers.
Puigdemont has been due to leave Finland on Saturday afternoon, but his exact whereabouts were unknown.
Five people are held in custody, including Catalan presidential candidate Jordi Turull who was due Saturday to seek a second round vote in the regional parliament, after failing to be elected earlier in the week.
Former Catalan leader Carles Puigdemont will speak at the International Film Festival and Forum on Human Rights in Geneva.
During last year's secession crisis in the Spanish region, Vila, who was serving as Puigdemont's business minister, quit the day before Catalan lawmakers made a unilateral declaration of independence on October 27.
Some 45,000 people joined the "Republic Now" march called by the influential pro-independence citizens' group ANC.
Carles Puigdemont has endorsed the currently-detained Jordi Sànchez as his candidate of choice for the Catalan presidency.
Because many who support secession are in self-imposed exile or abstaining, the likelihood of the vote leading to Catalan independence is slim.
Carles Puigdemont's decision comes as a blow to Catalonia's secessionist movement.
Manchester City manager Pep Guardiola will stop wearing a yellow protest ribbon if the Premier League-leading club's officials ask him to or if it adversely affects the team's form.
The Mobile World Congress, currently taking place in Barcelona, has been overshadowed by the ongoing issue of Catalan secession.
Anna Gabriel fled to Switzerland to avoid attending a court hearing, which she believed would be unfair.
Catalonia's quest for independence continues to pit it against the Spanish government and judiciary.
Catalonia's parliament will meet without Carles Puigdemont, who is in self-imposed exile in Belgium.
Spanish Prime Minister Mariano Rajoy also denied the idea of Carles Puigdemont leading Catalonia from exile, should he be elected president of Catalonia.
A new regional election will be held in Catalonia on Dec 21, says country's Prime Minister Mariano Rajoy in a televised address on a day of high drama.
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