Hundreds of thousands of flag-waving demonstrators packed central Barcelona on Sunday to rally against plans by separatist leaders to declare Catalonia independent following a banned secession referendum.
Catalans calling themselves a "silent majority" opposed to leaving Spain broke their silence after a week of mounting anxiety over the country's worst political crisis in a generation.
The crowd waved both Spanish and Catalan flags and chanted "Viva Espana! Viva Catalonia!" as they made their way through the streets of Barcelona under a clear blue sky.
"We have perhaps been silent too long," Alejandro Marcos, 44, told AFP.
"It seems that the one who yells the most wins the argument. So we have to raise our voices and say loud and clear that we do not want independence."
Around 350,000 people attended the rally, municipal police said, while organisers put turnout at between 930,000 and 950,000.
Some protesters called for the region's separatist president Carles Puigdemont to go to jail for holding a vote on independence in defiance of the Spanish government and courts.
"The unity of Spain cannot be voted on or negotiated -- it must be defended," read one sign in the crowd.
Others called for dialogue. The slogan for the demonstration -- organised by the Societat Civil Catalana, the main anti-independence group in Catalonia -- was: "Enough, let's recover good sense!"
- Rajoy's stern warning -
Recent polls had indicated that Catalans are split on independence, though leaders said police violence during the referendum turned many against the state authorities.
City police said 700,000 people joined a pro-independence protest in Barcelona two days after the vote.
On the eve of the rally, Spain's Prime Minister Mariano Rajoy issued a stern warning to Catalan leaders who have said they could declare independence this week.
He did not rule out moving to stop that by suspending Catalonia's regional autonomy -- a move that could risk sparking unrest.
"I rule out absolutely nothing that is allowed for under the law," he said in an interview with El Pais newspaper.
"The ideal would be not to have to take drastic measures," he said.
"I would like this threat of a declaration of independence to be withdrawn as quickly as possible."
- 'Still time' -
Tensions soared after police cracked down on voters during the banned October 1 independence referendum, prompting separatist leaders to warn they would unilaterally declare independence.
Tentative signs emerged Friday that the two sides may be seeking to defuse the crisis after Madrid offered a first apology to Catalans injured by police during the vote. 
But uncertainty still stalks the country as Catalan leaders have not backed off from plans to declare the region independent.
Puigdemont is scheduled to address the regional parliament on Tuesday evening.
It remains unclear what he plans to say, although some separatist leaders hope he will use the opportunity to declare independence.
Rajoy assured Catalan leaders that there "is still time" to backtrack and avoid triggering a tough response from the central government in Madrid.
- 'Traitors' -
With its own language and cultural traditions, demands for independence in Catalonia date back centuries but have surged during recent years of economic hardship.
The latest crisis has raised fears of unrest in Catalonia, a northeastern region about the size of Belgium that is home to 7.5 million people and accounts for a fifth of Spain's economy.
Spanish police caused international shock by beating voters in the October 1 referendum.
At Sunday's rally, demonstrators cheered and applauded when a national police helicopter flew over and some people shook the hands of national police officers to thank them for their efforts to stop the referendum.
But protesters jeered members of Catalonia's regional police force, the Mossos d'Esquadra, which had largely ignored a court order to close polling stations and seize ballot boxes.
Dozens of protesters surrounded two Mossos vans and called the officers standing on guard in front of them "traitors". 
- Nobel warning -  
Nobel literature prize winner Mario Vargas Llosa warned in an address to the crowd at the end of the rally that "passion can be destructive and ferocious when it is fueled by fanaticism and racism."
"The worst of all, the one that has caused the most ravages in history, is nationalist passion," he added.
The Catalan government on Friday published final results from the referendum indicating that 90 percent of voters backed the proposal to break away from Spain.
Turnout was 43 percent as Catalans who reject independence largely boycotted the polls.
The vote was not held according to official electoral standards as there were not regular voter lists, electoral commission or observers.
Protesters piled off the morning train from Madrid at Barcelona's Sants station to join the protests on Sunday.
"I'm tired of being quiet," said Susana Cerezal, 41, who came to the demonstration from the town of Figueras near the border with France.