The people of Catalonia voted overwhelmingly in favour of a statute giving it more autonomy.
According to official data, with 98.5 per cent of the votes counted, 73.9 per cent of Catalans said "yes" to a fiercely contested statute that has fired debate on autonomy in Spain's regions and reawakened sensitivities that date back to the civil war of the 1930s.
A low turnout in the ballot immediately sparked questions about its validity: Just under half of the five million Catalans eligible to vote did so, with 50.6 per cent abstaining from the ballot.
The leader of the right-leaning main opposition party, Mariano Rajoy, said the result showed a lack of support for the central government-backed project.
"This has been a demonstration of common sense. . . . Catalans have not supported [Prime Minister Jose Luis Rodriguez] Zapatero's personal project, two out of
three of them were not in favour," Mr Rajoy said, counting those who abstained as equal to a "no" vote.
The referendum gives Spain's wealthiest region a greater slice of its income tax and more spending is considered a test of strength of the central government.
The statute has been the subject of bitter dispute between regional and national political parties for more than a year, centring on a phrase that says Catalonia perceives itself as "a nation".
Compromise on that phrase in the final statute was eventually rejected by both ends of the political spectrum - the right-leaning Popular Party (PP), which says it is a threat to Spanish unity, and the Catalan nationalist party Esquerra Republicana, which says it does not go far enough.
Mr Zapatero's government, seen as inclined to give more autonomy to Spain's already powerful regions, campaigned for a "yes" result.