In his first public pronouncement since the divisive referendum, the president of the Catalan region, Carles Puigdemont, said his government would declare independence in a matter of days.
He told the BBC that his government would "act at the end of this week or the beginning of next", and said that if the Spanish central government tried to intervene, it would be an "error which changes everything".
Amid huge rallies taking place across Catalonia, the country's king, Felipe VI denounced the organisers of the referendum as it showed "disrespect to the powers of the state.
"They have broken the democratic principles of the rule of law. Today, the Catalan society is fractured," he said on Tuesday (3 October).
"These authorities have scorned the attachments and feelings of solidarity that have united and will unite all Spaniards. Their irresponsible conduct could even jeopardise the economic and social stability of Catalonia and all of Spain," he said.
There were reports of a turnout of around 700,000 people in a demonstration in Barcelona, while the city endured road blocks, traffic jams and train delays.
Some 33 police officers were said to be injured in the mass action following the referendum whose organisers said saw a 90% approval for the north east region to declare independence.
Turnout did not exceed 40%. The Spanish government has said it would respond with "all necessary measures" should the region declare independence.