Update 9.19pm: The Catalan authorities have deliberately bent the law with their "irresponsible conduct", Spain's King Felipe VI has said.
He said the state needs to ensure constitutional order and the rule of law in Catalonia.
King Felipe spoke out as tens of thousands of people joined marches across Barcelona in protest against the Spanish government's actions over the region's independence vote.
Delivering an address to the nation by television, the king said that the bid by authorities in the north-eastern region to push ahead with independence has "undermined coexistence" in Catalonia.
"Today, Catalan society is fractured and confronted," Felipe said, referring to the political crisis as "very serious moments for our democratic life".
He said the state needs to ensure Spain's constitutional order and the correct functioning of Catalan institutions and rule of law.
Spain's conservative government has said it will respond with "all necessary measures" to counter the Catalan defiance.
It is holding talks with national opposition leaders to try to find consensus on the response, which could include suspending the region's self-government.
Earlier: Tens of thousands of people are joining marches across Barcelona in protest against the Spanish government's actions over the region's independence vote.
Separatist groups and unions had initially called for strikes to be held on Tuesday in support of Catalan leaders pushing ahead with a declaration of independence from Spain. But many non-separatists were also drawn to the streets following a crackdown on a referendum vote on Sunday.
The main national unions, CCOO and UGT, rejected the strike but told workers to join protests.
In Barcelona's Catalonia and University squares, a sea of demonstrators waved flags, most of them "esteladas," embraced by those seeking secession, but there were also plenty of Spanish national flags.
Among many banners displayed, one read "Stop violence, #CataloniaIsComing" and another one wondered "Where are you Europe?"
One of the biggest groups concentrated around the Spanish national police headquarters in Barcelona, where protesters called them "occupying forces" and called for Prime Minister Mariano Rajoy to resign.
Earlier Barcelona's football stars were among workers in Catalonia to down tools.
The club said none of its professional or youth teams were training and the club base was closed.
Girona's team also did not train while Espanyol's players underwent physical exercises behind closed doors.
Barcelona defender Gerard Pique, one of the most outspoken supporters of Catalonia, was harassed by fans on Monday when he reported to Spain's national team training camp in Madrid ahead of upcoming World Cup qualifiers.
Several hundred Barcelona port workers held a demonstration outside the regional headquarters of Spain's ruling Popular Party chanting slogans against government policies and the alleged brutality of police during Sunday's polling day.
The port workers threw wads of unused ballot papers from the vote into the air in the protest outside the party's office in Barcelona.
Regional police placed barriers outside the building to stop the crowd getting near the offices and the protest lasted more than an hour.
Madrid's top official in Catalonia said he lamented the violence but blamed the regional separatist government for "exposing citizens to danger".
Enric Millo said on Tuesday "nothing of this would have happened if the government wouldn't have declared itself in rebellion, breaking the orders of the courts and lying and tricking people".
He said Spain's National Police and Civil Guard anti-riot squads broke into schools designated as polling stations when it was clear that the regional Mossos d'Esquadra police, controlled by the Catalan government, was not carrying out a judge's orders to impede the voting.
He also accused the grassroots groups driving the independence bid, the National Catalan Assembly and Omnium Cultural, and pro-independence mayors of "plotting to break the law".