"We have perhaps been silent too long", Alejandro Marcos, 44, told AFP.
"Many people believe - and he seems to be moving in that direction - that he will use this opportunity to declare, or to announce the results of the referendum which, as far as he was concerned, were overwhelmingly in favor of independence", Dominic Thomas, chair of the department of French and francophone studies at the University of California Los Angeles, told CNN. "We will see what happens this week but we have to speak out very loudly so they know what we want".
Image: Organisers claimed a million people joined the march.
"Spain will not be divided and the national unity will be preserved".
Careful not to undermine Rajoy, the European Union has merely called for dialogue between the sides. There is no certain confirmation of this move, however, with Catalan lawmakers unofficially saying that they will stop short of the independence declaration, opting for more of a "symbolic statement".
Under Catalonia's referendum law, deemed unconstitutional by Madrid, a vote on Tuesday would start a six-month process that would envisage divorce talks with Spain before regional elections and a final act of separation.
On Saturday, thousands of protesters gathered at rallies in Barcelona, Madrid and other Spanish cities to demand dialogue to end the dispute.
German Chancellor Angela Merkel has stressed her backing for the "unity of Spain" in a phone call with Prime Minister Mariano Rajoy amid a threat by Catalan separatists to declare independence, her spokesman said Monday.
The ideal would be not to have to take drastic measures.
Catalonia held a disputed referendum on October 1, in which 90 per cent of participating Catalans voted for secession.
The vote had been declared illegal in Madrid before it even took place, and violent clashes erupted with police at polling stations.
That raises the prospect of Spanish police arresting Puigdemont and other separatist leaders if they declare independence.
"Any attempt by the state to entirely disempower the regional government and regional parliament will probably be met by mass mobilizations and more unrest", wrote Federico Santi, an analyst at consultancy Eurasia Group.
Initially it was thought separatist leaders could move to declare independence as early as Monday night, but the address has been pushed back a day.
But Rajoy assured Catalan leaders that there "is still time" to backtrack and avoid the imposition of direct rule.
Catalonia accounts for almost a fifth of Spain's economy, and leads all regions in producing 25% of the country's exports, CNNMoney reports.