Spain's King Felipe VI has said Catalan authorities deliberately bent the law with "irresponsible conduct" in Sunday's vote and the Spanish state needs to ensure constitutional order and the rule of law in Catalonia.
- King condemns Catalan independence vote as 'irresponsible'
- Spain's Constitutional Court ruled Sunday's vote illegal
- Workers stage strikes across Catalan region
Delivering an address to the nation by television, the king said the bid by authorities in the north-eastern region to push ahead with independence has "undermined coexistence" in Catalonia.
His comments came after Catalan's regional government held a vote on independence on Sunday that Madrid had ruled illegal.
"Today, Catalan society is fractured and confronted," King Felipe said.
He referred to the political crisis as, "very serious moments for our democratic life," and said the state needed to ensure Spain's constitutional order and the correct functioning of Catalan institutions and rule of law.
He said the Spanish crown was strongly committed to the Spanish constitution and to democracy and underlined his commitment as king "to the unity and permanence of Spain".
Catalonia, Spain's richest region, has its own language and culture and a political movement for secession that has strengthened in recent years.
About 900 people were injured on polling day when police fired rubber bullets and charged at crowds with truncheons to disrupt the vote.
Those who participated voted overwhelmingly for independence, but opinion polls conducted before the vote suggested only a minority of about 40 per cent of residents in the region back independence.
Catalan leader Carles Puigdemont said the referendum was valid and its result must be implemented.
Spain's conservative government said it would respond with "all necessary measures" to counter the Catalan defiance, and was holding talks with national opposition leaders.
A multi-partisan consensus on the response could include suspending the region's self-government.
Protests continue amid strikes
Tens of thousands of people continued to take to the streets of Catalonia and road traffic, public transport and business were disrupted in protest against Sunday's violent crackdown.
Metro stations shut down in Barcelona, pickets blocked dozens of roads and state workers walked out in response to a call for a general strike by pro-independence groups and trade unions.
FC Barcelona, the city's football club, joined the strike, saying it would close for the day and none of its teams would train.
On financial markets, Spain's 10-year borrowing costs hit their highest level in nearly three months.
To the north of Barcelona, a line of tractors moved down a road blocked to traffic, accompanied by protesters chanting "Independence" and, "The streets will always be ours".
Crowds gathered outside the local headquarters of Spain's ruling People's Party and the Spanish national police headquarters in Barcelona, whistling and waving the red-and-yellow regional flag.
Barcelona tourist attractions such as museums and architect Antoni Gaudi's Sagrada Familia church, were shut.
Carmaker SEAT, owned by Germany's Volkswagen, was forced to halt production on one of three production lines at its plant because the road closures interrupted supply of a part, but operations later resumed.
Spain's Deputy Prime Minister, Soraya Saenz de Santamaria, said the regional government had lost respect for the democratic process and were showing a flagrant disregard for the law.
"I've seen how President [Carles] Puigdemont has flooded the streets with his followers to stop people obeying the law and to make them disrespect justice," she said.
"We are here to defend the rights and liberties of all Spaniards that have been trampled upon by the regional government."