Catalan government head Artur Mas called the vote, which was ordered blocked by the constitutional court at Madrid's request, "a total success" after the overwhelming majority of those who took part supported independence.
"Catalonia has once again, the people of Catalonia, have made it very clear that we want to govern ourselves. It is an old aspiration, which dates back centuries and remains perfectly alive," he added in Barcelona after polls closed.
Preliminary results released by the Catalan government showed 80.7 per cent of participants -- or about 1.6 million people -- voted for independence.
Anti-independence parties largely boycotted the referendum, which was organised by an army of volunteers, skewing the results in favour of a break from Spain.
The government also forecast that final turnout figure would be 2.25 million voters despite legal challenges and objections from the central government in Madrid to the ballot.