Catalan leader Carles Puigdemont says the Spanish region has won the right to statehood following a contentious referendum that was marred by violence.
He said the door was open to a unilateral declaration of independence after Catalan officials said voters had backed secession with a 42.3% turnout.
Spain's government has warned it could suspend Catalan autonomy.
The constitutional court banned the vote and almost 900 people were hurt as police tried to stop it going ahead.
Officers from the national police and paramilitary Civil Guard seized ballot papers and boxes at polling stations.
Spanish Prime Minister Mariano Rajoy said Catalans had been fooled into taking part in an illegal vote.
More than 2.2 million people were reported to have voted, according to Catalan authorities, out of 5.3 million registered voters. Just under 90% of those who voted backed independence, they said.
A Catalan spokesman said more than 750,000 votes could not be counted because polling stations were closed and urns were confiscated.
"With this day of hope and suffering, the citizens of Catalonia have won the right to an independent state in the form of a republic," Mr Puigdemont said in a televised address.
"My government in the next few days will send the results of today's vote to the Catalan parliament, where the sovereignty of our people lies, so that it can act in accordance with the law of the referendum."
The Spanish prime minister spoke of a "mockery" of democracy.
"At this hour I can tell you in the strongest terms what you already know and what we have seen throughout this day. There has not been a referendum on self-determination in Catalonia," Mr Rajoy said.
Spain's justice minister warned that any declaration of independence could lead to article 155 of the country's constitution being invoked which allows the national government to intervene in the running of an autonomous region.
"We are not here to divide Spaniards... but if someone tries to declare independence on behalf of a part of Spain's territory, that cannot be done because it is beyond their powers," said Rafael Catalá.
More than 40 trade unions and Catalan associations called a region-wide strike on Tuesday due to "the grave violation of rights and freedoms".
Catalan medical officials said 844 people had been hurt in clashes, including 33 police. The majority had minor injuries or had suffered from anxiety attacks.