Catalan separatists burned barricades and clashed with police in Barcelona on Thursday in a fourth night of violence triggered by Spain's jailing of nine of their leaders over a failed independence bid.

Hundreds of young protesters chanting "independence" set fire to improvised roadblocks in the centre of the city late in the evening, tossing Molotov cocktails at police, who responded by firing foam and anti-riot rounds, according to AFP correspondents.

Around 25,000 students rallied in central Barcelona as they began a strike in protest over the verdicts
Around 25,000 students rallied in central Barcelona as they began a strike in protest over the verdicts AFP / Pau Barrena

The fresh clashes came on the eve of a huge protest planned in the Catalan capital. Separatists have called a general strike and a rally on Friday against the Supreme Court's decision to jail the separatist leaders for their role in a referendum banned by Madrid and a short-lived declaration of independence.

Earlier on Thursday, around 25,000 striking students and their supporters took part in a midday rally outside Barcelona city hall, according to municipal police. Thousands more are on a cross-country march towards Barcelona for Friday's rally.

"The actions we have been staging over the past few days testify to the helplessness we feel as the Spanish state continues to reject (independence) and threaten us, while Europe remains silent," a 23-year-old accountant, who would only give his first name as David, told AFP.

There have been mass marches and rallies every day since the verdict was announced on Monday morning
There have been mass marches and rallies every day since the verdict was announced on Monday morning AFP / Pau Barrena

Eduard Salinero, a 21-year-old physics student who is in favour of secession, said many people who want Catalonia to remain a part of Spain back the protests "because they feel it is totally unfair to send our elected politicians to jail".

Activists blocked several roads across Catalonia by burning tyres while the commuter rail service in Barcelona was intermittently disrupted due to demonstrators on the tracks, officials said.

Catalan president Quim Torra has pledged to work for a new independence referendum before his term ends in early 2022
Catalan president Quim Torra has pledged to work for a new independence referendum before his term ends in early 2022 AFP / Josep LAGO

Several roads and highways were also blocked off due to the mass marches which departed on Wednesday from five Catalan towns heading for Barcelona.

Xenia Cabeza, 18, said she was protesting "because they don't let us vote in a referendum" on secession. She carried a sign that read "You can't imprison an entire people".

Announced Monday morning, the verdict has sparked three days of large demonstrations which have turned increasingly violent with separatist activists engaged in nighttime clashes with riot police in Barcelona and elsewhere.

AFPTV / Maud WATINE

'No impunity'

Overnight, protesters in Barcelona set fire to cars and large wheelie bins, overturned metal barriers and threw firecrackers at police, who pushed back with batons and shields.

Emergency services said 58 people were injured, including a 17-year-old who was hit by a police van.

Another 38 people were injured in protests in other Catalan cities, including Lerida and Girona.

Hundreds of young protesters chanting 'independence' burned barricades in the centre of Barcelona
Hundreds of young protesters chanting 'independence' burned barricades in the centre of Barcelona AFP / LLUIS GENE

Police have arrested 97 people across Catalonia since the protests began, Interior Minister Fernando Grande-Marlaska said Thursday.

"We are experiencing episodes of great violence in Catalonia carried out by minority groups which are perfectly organised," he said, vowing there would be "no impunity" for those involved in the violence.

Berta Barbet, a political scientist at the University of Barcelona, said the demonstrations "in their current size" would likely only last a week.

"We are talking about actions that take a lot of time and energy and I don't see a big part of the population keeping it up for long," she told AFP.

'Push forward'

While Catalan president Quim Torra has sanctioned and even encouraged civil disobedience, his government is also responsible for the regional police who are charged with controlling demonstrations, putting him in an uncomfortable position.

Torra had not commented on the unrest for days, but overnight he called for an immediate halt to the violent clashes, saying there was "no reason or justification for burning cars".

But just hours later, he pledged in Catalonia's regional parliament to push for a new vote on secession by the end of his term in early 2022.

"We must push forward and not allow ourselves to be intimidated by threats and bans," he said.

A poll published in July by a public Catalan institute showed support for an independent Catalonia at its lowest level in two years, with 48.3 percent of people against and 44 percent in favour.

The court's decision has thrust the Catalan dispute to the heart of the political debate ahead of Spain's November 10 general election, its fourth in as many years.

The main opposition conservative Popular Party, which takes a hard line on Catalan separatists, looks set to make significant gains, it found.

Published in El Mundo daily, it predicted the Socialists will capture 122 seats in the 350-seat parliament, compared with the 123 it took in the last election in April, while the PP would win 98 seats, up from 66.