Spain's King Felipe VI has condemned organisers of Catalonia's independence referendum for having put themselves "outside the law".
About 700,000 people took to the streets of Barcelona in protest at police actions during Sunday's referendum Photo: AFP
In a TV address to the nation, he said the situation in Spain was "extremely serious", and called for unity.
Hundreds of thousands in Catalonia have been protesting over Spanish police violence during Sunday's vote, during which nearly 900 people were hurt.
There is little public transport across the region, after local trade unions called a strike.
The central government in Madrid said the referendum was illegal.
During the vote, 33 police officers were also injured, local medical officials said.
In his address, King Felipe VI said Catalan leaders who organised the referendum showed their "disrespect to the powers of the state".
"They have broken the democratic principles of the rule of law.
"Today, the Catalan society is fractured," the king said, warning that the poll could put at risk the economy of the wealthy autonomous north-eastern region and the whole of Spain.
But he said that Spain "will overcome difficult times".
About 700,000 people have taken to the streets in Barcelona, city police were quoted as saying by the AFP news agency.
More than 50 roadblocks in the city caused big traffic jams. Barcelona's metro traffic was cut to a 25 percent service during rush hour and no trains at all at other times.
Barcelona's port was at a standstill, trade union sources said.
Top tourist attractions were also closed, including the city's famous Sagrada Familia church.
Protest rallies are also taking place in other major cities and towns of the north-eastern autonomous region.
The strike was called in protest at "the grave violation of rights and freedoms" seen during Sunday's ballot.
Some police officers were seen firing rubber bullets, storming into polling stations and pulling women by their hair.
Central govt condemns regional leaders
Spanish Prime Minister Mariano Rajoy has said the vote made a "mockery" of democracy.
On Tuesday, Spanish Interior Minister Juan Ignacio Zoido said: "We see how day after day the government of Catalonia is pushing the population to the abyss and inciting rebellion in the streets."
He also warned that the central government would take "all measures necessary to stop acts of harassment".
On Sunday, more than 2.2 million people reportedly voted in the referendum. The Catalan government says the vote in support of independence was nearly 90 percent, but official results have not yet been released.
Turnout was relatively low at a reported 42 percent, potentially weakening the position of Catalan President Carles Puigdemont.
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.
Meanwhile, political leaders are trying to find a way forward.
Mr Puigdemont has said he wants a new understanding with the central government in Madrid, but the Spanish government has warned it could suspend autonomy of the wealthy north-eastern region.
Mr Rajoy held talks with Pedro Sánchez, leader of Spain's main opposition Socialist party, as well as Albert Rivera, the head of the centrist Ciudadanos party, late on Monday.
While the Socialist leader urged Mr Rajoy to hold talks with the Catalan president immediately, Mr Rivera said Spain should invoke article 155 of the constitution, in effect suspending Catalonia's autonomous powers.
Mr Puigdemont has called on the international community to help mediate between the two sides.
However, the European Commission described the crisis as "an internal matter" for Spain, that has to be dealt with in line with the constitutional order.
-BBC