"There's no going back now... the days to come will be complicated, but we have to resist", David Peña, an activist in Catalonia, said.
Felipe said the referendum's organisers showed "disrespect to the powers of the state", but made no mention of Sunday's violence.
"On Sunday we had a referendum under the most hard circumstances and set an example of who we are".
"We are to declare independence 48 hours after all the official results are counted", he said in an interview with the BBC.
Schools and some businesses also shut in a dramatic protest bound to further ratchet up fever-pitch tensions with Spain's central government, as Madrid comes under growing worldwide pressure to resolve its worst political crisis in decades.
In response, King Felipe VI accused Catalan leaders of shattering democratic principles and dividing society. Catalonia's planned referendum on secession is due to be held Sunday by the pro-independence Catalan government but Spain's government calls the vote illegal, since it violates the constitution, and the country's Constitutional Court has ordered it suspended.
Spain's Caixabank, Catalonia's largest lender, and ministers reassured bank customers that their deposits are secure from the growing crisis.
"In the case of independence, Catalan teams in La Liga - Barcelona, Espanyol and Girona - will have to decide where they want to play: in the Spanish league or a neighbouring country like Italy, France or England", he said.
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