Catalan leader Carles Puigdemont says the region has won the right to statehood following Sunday’s contentious referendum which was marred by violence.
He said the door had been opened to a unilateral declaration of independence.
Hundreds of people were injured as Spanish police used force to try to block voting.
The Spanish government had pledged to stop a poll that was declared illegal by the country’s constitutional court.
Police officers prevented some people from voting, and seized ballot papers and boxes at polling stations.
“With this day of hope and suffering, the citizens of Catalonia have won the right to an independent state in the form a republic,” Mr Puigdemont said in a televised address flanked by other senior Catalan leaders.
He said the European Union could no longer “continue to look the other way”.
Earlier, as voting ended, Spanish Prime Minister Mariano Rajoy said Catalans had been fooled into taking part in an illegal vote. He called it a “mockery” of democracy.
Large crowds of independence supporters gathered in the centre of the regional capital Barcelona on Sunday evening, cheering and waving Catalan flags.
The Catalan government said more than 800 people had been injured in clashes across the region.
The Spanish interior ministry said 12 police officers had been hurt and three people arrested. It added that 92 polling stations had been closed.
A total of 337 people visited hospitals and health centres, a spokeswoman for the Catalan government’s health department said.