With the angry demonstrations entering their fifth day, activists blocked a string of roads in the wealthy northeastern region, cutting off the main cross-border highway with France.

Workers were also downing tools against Monday's Supreme Court verdict in which the separatist leaders were handed long jail terms over a banned referendum and an abortive independence declaration two years ago.

As well as the strike, tens of thousands of people streamed into Barcelona after a three-day march from five Catalan towns in a bid to cause chaos on the roads in a region that accounts for about a fifth of Spain's economic output.   

They were due to gather for yet another massive demonstration — expected to be the largest yet.

By early afternoon, thousands of striking students were marching through the city, waving signs reading: “We the people will not yield” and “Free the political prisoners”.

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“We have to push a bit more and we'll get what we want,” said 18-year-old Miquel Flores, a nursing student, referring to a referendum on independence.   

“The strength of the Catalan people is unstoppable.”   

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”.

“The criminal and violent behaviour we've seen in Barcelona is intolerable,” he said, insisting such unrest had “nothing to do with the separatist claim”.

And Barcelona city council said the first three days of clashes had cost an estimated €1,575,000 ($1,755,000) in damage, without taking into account Thursday's  vandalism.   

So far, more than 700 large wheelie bins have been torched, while mob violence had also damaged traffic lights, street signs, trees and the city's bike-share service, it said.

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