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.
Given the chaotic nature of the vote, the turnout and voting figures should be taken with a pinch of salt, says the BBC's Tom Burridge in Barcelona.
What have Catalan and Spanish leaders said?
"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.
What happens next?
Analysis: Tom Burridge, BBC News, Barcelona
Spain's complicated relationship with the region of Catalonia is headed for the unknown.
After violence by Spanish police, a declaration of independence by Catalonia's regional government seems more likely than ever before.
On Monday the government in Madrid will hold talks with Spanish parties to discuss a response to the biggest political crisis this country has seen in decades.
More than 40 trade unions and Catalan associations called a region-wide strike on Tuesday due to "the grave violation of rights and freedoms".
How bad was the violence?
TV images showed Spanish police kicking would-be voters and pulling women out of polling stations by their hair.
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.
- How Barcelona and Madrid viewed the vote
- The most powerful images of Catalan clashes
- The reasons for the referendum
In Girona, riot police smashed their way into a polling station where Mr Puigdemont was due to vote, and forcibly removed those inside. He voted at another station.
The BBC's Tom Burridge in Barcelona witnessed police being chased away from one polling booth after they had raided it.
TV footage showed riot police using batons to beat a group of firefighters who were protecting crowds in Girona.
The national police and Guardia Civil - a military force charged with police duties - were sent into Catalonia in large numbers to prevent the vote.
The Catalan police - the Mossos d'Esquadra - have been placed under Madrid's control, however witnesses said they showed little inclination to use force on protesters.
Barcelona Mayor Ada Colau, who voted blank on Sunday, condemned police actions against the region's "defenceless" population, but Spain's Deputy Prime Minister Soraya Saenz de Santamaria said police had "acted with professionalism and in a proportionate way".
Large crowds of independence supporters gathered in the centre of the regional capital Barcelona on Sunday evening, waving flags and singing the Catalan anthem. Anti-independence protesters have also held rallies in Barcelona and other Spanish cities.
How much voting took place?
Catalan authorities said 319 of about 2,300 polling stations across the region had been closed by police while the Spanish government said 92 stations had been sealed off.
Since Friday, thousands of people have occupied schools and other buildings designated as polling stations in order to keep them open.
Many of those inside were parents and their children, who remained in the buildings after the end of lessons on Friday and bedded down in sleeping bags on gym mats.
The anti-independence Societat Civil said there were voting irregularities, including the same people voting twice.
Catalonia, a wealthy region of 7.5 million people in north-eastern Spain, has its own language and culture.
It also has a high degree of autonomy, but is not recognised as a separate nation under the Spanish constitution.