Barcelona (AFP) - Hundreds of masked youths clashed angrily with police in Barcelona on the sidelines of a mass march which drew more than half a million people in protest over Spain’s jailing of nine Catalan separatist leaders.

It was the biggest gathering since Monday’s explosive verdict, which had already brought tens of thousands of independence supporters onto the streets in protest in this wealthy northeast region.

Police said 525,000 people had joined Friday’s giant protest, the latest in a mass show of anger after Spain’s Supreme Court sentenced nine separatists to long jail terms over a banned referendum and an abortive independence declaration two years ago.

But while most marchers appeared peaceful, hoards of young protesters went on the rampage in Via Laietana, setting a huge blaze which sent plumes of black smoke into the air, as police fired teargas to disperse them, an AFP correspondent said.

“Anti-fascist Catalonia!” they roared. “The streets will always be ours!”

Elsewhere among the crowds were many thousands of “freedom marchers”, who had set out from five regional towns on Wednesday to walk to the Catalan capital, many wearing walking boots and carrying hiking poles.

The rally coincided with a general strike, prompting the cancellation of 57 flights, the closure of shops, business and several top tourist attractions, and slowing public transport to a trickle in a region that accounts for about a fifth of Spain’s economic output.

Activists also cut off Catalonia’s main cross-border highway with France.

- ‘Jailed like murderers’ -

In downtown Barcelona, many shops and luxury outlets were closed on the city’s Paseo de Gracia, with blackened, charred patches a testimony to the nightly clashes that have raged every evening since Monday.

“With these demonstrations bringing this large city to a halt, we are using Barcelona like a microphone,” said 23-year-old engineering student Ramon Parada.

“It’s all in reaction to the injustice of the verdict against politicians and civil leaders who acted peacefully but were sentenced to between nine and 13 years of prison, like murderers,” he said.

Retired lawyer Jaume Enrich agreed, saying the sentence was “the straw that broke the camel’s back.”

“Madrid is putting Spanish unity above everything, including basic rights,” he told AFP, wearing a badge saying “No surrender”.

Nearby a banner fluttered reading “There are not enough cages for this many birds.”

- Clashes and closures -

The huge turnout came after yet another night of violent clashes, which Catalan regional interior minister Miquel Buch said involved “fewer incidents, but more violent”.

And Barcelona city council said the first three days of clashes had cost an estimated 1,575,000 euros ($1,755,000) in damage, with more than 700 large wheelie bins torched and mob violence also damaging traffic lights, street signs, trees and the city’s bike-share service.

In Barcelona, Spain’s top tourist destination, the Sagrada Familia basilica closed as protesters massed outside, and the famous Liceu opera house cancelled Friday night’s performance.

Barcelona’s huge wholesale market, which exports around a third of the region’s fresh produce, was barely trading on Friday, and at the city’s famed La Boqueria market, most of the stalls were closed.

At one stall, Barcelona-born Susana Medialdea, 53, was selling olives and pickles entirely dressed in yellow.

“I came in voluntarily to work but only as long as I could wear yellow to express my total disagreement with the sentence,” she told AFP, saying she felt “very angry” about it.

But another veteran stallholder took the opposite view.

“I am real Catalan but I don’t support this independence project at all, people are letting themselves be used, above all the youth,” said 75-year-old Carmen Isern, accusing the secessionists of dishonesty.

“We’ve had seven years of lies. They only tell the teenagers bad things about Spain.”

- Spain’s Clasico clash postponed -

Across the region, many roads were blocked by demonstrators, burning barricades and in one case, activists threw nails on the ground, puncturing tyres on passing cars.

With the region mired in chaos, football authorities cancelled the Barcelona and Real Madrid Clasico set for October 26 at the Camp Nou stadium. Both clubs had reportedly refused an offer to hold the match in Madrid.

And Manchester City’s Catalan manager Pep Guardiola, an outspoken campaigner for the independence movement, urged European intervention to ease the crisis.

“The international community must help us to solve the conflict between Catalonia and Spain,” he said on Friday. “Some mediator from outside (must) help us sit (down) and talk.”

The Supreme Court’s explosive decision has thrust the Catalan dispute to the heart of the political debate as Spain heads towards a fourth election in as many years, which will be held on November 10.