Protests erupted in Catalonia early on Tuesday, a day after Spain's Supreme Court sentenced nine pro-independence Catalan leaders to prison terms of up to 13 years for sedition and other offences.
Several highways in the region were cut off by demonstrators and high speed trains between Barcelona and Girona remained disrupted after damage to the tracks by protesters on Monday.
Local emergency services reported on Monday night that 78 people had been injured, almost all of them in clashes between protesters and police in Barcelona airport, as tensions rose ahead of Spain's November 10 general election.
The Supreme Court case centred on the illegal independence referendum held in Catalonia on October 1 2017, which the then regional authorities held despite the constitution's provisions on the "indissoluble unity of the Spanish nation", and a subsequent unilateral declaration of independence.
The court found the chief defendants guilty of sedition, leading what it characterised as an uprising that undermined the rule of law, but not of the graver offence of rebellion.
It sentenced Oriol Junqueras, the former deputy leader of the region's government, to 13 years in prison for sedition and misuse of public funds.
Six other former Catalan officials were sentenced to 10 to 12 years. Two Catalan politicians who headed pro-independence organisations were sentenced to nine years each. Three other defendants were fined and barred from public office for 20 months.
Pablo Llarena, the prosecutor in the case, responded to the sentencing by reactivating his request for the extradition of Carles Puigdemont, the former head of the Catalan government, who has fled to Belgium.
"Today's decision confirms the defeat of a movement that failed to gain internal support and international recognition," said Pedro Sánchez, Spain's caretaker prime minister, who accused the separatists of ignoring an anti-independence majority within Catalonia.
But the authorities, both Catalan and Spanish, were immediately tested by the response to the verdict, as thousands of protesters marched to Barcelona airport and elsewhere. Aena, the Spanish airports operator, said airlines had cancelled more than 100 flights because of blocked transport links while police charged to remove protesters from the area.
In contrast with the sequence of events in 2017, when Madrid temporarily took over the administration of the region, Mr Sánchez said his government would "respond proportionally to any violations of the law" and would seek dialogue "within the boundaries of the law and the Spanish constitution".
But Quim Torra, head of the pro-independence Catalan government, labelled the sentencing "a verdict against millions of Catalans" and an act of vengeance rather than justice.
"We reaffirm our commitment . . . to move forward with no excuses, on the path to the Catalan republic," Mr Torra said. He called for an amnesty for the defendants, a step the government has ruled out, and called for urgent meetings with both Mr Sánchez and King Felipe VI. He later thanked the protesters for showing their solidarity with the defendants.
At present, Mr Torra's administration has not indicated it will break Spanish law in response to the verdict, and the Mossos d'Esquadra, the regional police force, warned that entering restricted areas in the airport was a serious crime.
Both Mr Sánchez and Mr Torra delivered versions of their remarks in English - an indication of the importance of international public opinion in the case.
In its decision, the court found there was insufficient violence to warrant the charge of rebellion, which prosecutors had sought but which Mr Sánchez's government had opposed.
The judgment described the 2017 independence attempt as a "mere pipe dream", given the Spanish state's control of the military, police and judiciary. Instead, it said "the imaginary right of self-determination was a device . . . to pressure the national government to negotiate a plebiscite".
It depicted the events of October 1 as "a riotous uprising, encouraged by the defendants, among many others, so as to use physical force and de facto coercion to turn court decisions of the constitutional court and of the high court of justice of Catalonia into a dead letter".
In a further sign of the international dimension of the dispute, Pep Guardiola, the manager of Manchester City football club, made a video appeal in English circulated by a Catalan activist group. He labelled the sentences "a direct affront to human rights" and denounced what he called Spain's "drift towards authoritarianism".