A car burns during a protest after a verdict in a trial over a banned Catalonia's independence referendum in Barcelona, Spain, October 16, 2019. Photo: VCG

Catalan leader Quim Torra called for an immediate halt to the violent clashes that rocked Barcelona for a third day Wednesday, warning they were harming the image of the separatist movement.

As the Catalan capital echoed with the sound of sirens and masked youths staged running battles with riot police, Spain's Pedro Sanchez had made a direct appeal to Torra to "clearly condemn" the violence. 

Earlier on Wednesday, thousands gathered for a protest called by the radical Committees for the Defence of the Referendum. 

But as the evening wore on, the situation quickly became chaotic, with hundreds running through the streets, hurling broken paving stones, torching cars and occasionally stopping to take selfies in front of the burning barricades. 

"This isn't violence, it's self-defence," roared a group of masked youngsters in front of a blazing barricade. 

Some even threw Molotov cocktails, the regional police said, with scenes of violence also spreading to other cities in the region such as Tarragona and Leida, prompting the Catalan leader to give a televised address shortly after midnight. 

"This has to stop right now," Torra said. 

"There is no reason or justification for burning cars, nor any other vandalism. Protest should be peaceful.

"We cannot allow such groups who infiltrate and provoke to harm the image of a movement which counts millions of Catalans," he added. 

Until now, Torra has not made any comment on the violence which erupted on Monday just hours after the Supreme Court handed down heavy prison sentences to nine Catalan leaders for their role in the failed independence bid of 2017. 

So far, Madrid has shown little appetite for taking matters into its own hands, despite the ongoing protests in Barcelona and elsewhere that have hit screens around the world as Catalan separatists have made their anger known.