In a defiant challenge to plans by Catalonia's regional government to unilaterally declare independence, hundreds of thousands of people flooded the streets of Barcelona in a surprising outpouring of Spanish unity.
They waved Spanish and Catalan flags and carried banners saying "Together we are stronger" and "Catalonia is Spain".
Other demonstrations - including in the Catalan city Barcelona - have also been held urging political dialogue.
"If there were a declaration of independence it would be unilateral and it wouldn't be recognised", Nathalie Loiseau said on CNews digital news channel.
The Catalan law paving the way for the referendum said the parliament of Catalonia would declare the region's independence within 48 hours of a "yes" vote being proclaimed by the Catalan electoral office.
More than 90 per cent of the 2.3 million people who voted backed secession, according to Catalan officials.
Instead, Catalan president Carles Puigdemont would make a "symbolic statement" and speak of embarking on a path leading towards independence. "I believe we know what Spaniards think, and they should know that the government too is clear about what it has to do", he said.
Meantime, a senior member of the Catalan administration called for dialogue with Spain, warning that all of Europe faces economic damage unless a resolution is found to his region's standoff with the central government in Madrid.
Madrid sent thousands of national police to the region to prevent the vote. Residents, some 7.5 million people, have also been able to maintain their national language: Catalan. About 900 people were injured when officers used rubber bullets and batons against voters in scenes that shocked Spain and the world, and escalated the dispute. "A period of prolonged and elevated tension in Catalonia or political uncertainty in Spain at large could weigh negatively on the economy and public finances".
Despite the outrage, Rajoy and even Spanish King Felipe VI defended the police and doubled down on their stance to take whatever measures necessary to keep Catalonia from seceding.
The boards of Catalonia-based infrastructure firm Abertis, telecoms company Cellnex and property group Inmobiliaria Colonial will meet on Monday to discuss moving, sources said.
Some of the demonstrators took to rooftops, including families with children, and leaned over ledges from their perches overlooking the streets below to wave giant Spanish flags in a city accustomed to the prevalence of the Catalan pro-independence estelada.
"The turnout in Barcelona and across Spain to talk about Spain and unity and to express the voice of those who would not want this referendum to go ahead was also overwhelmingly powerful".
Until this weekend, Rajoy has remained vague on whether he would take the unprecedented step of triggering Article 155 of the constitution, the so-called nuclear option which enables him to sack the regional government and call a local election.