Barcelona is bracing for a fifth day of protests over the conviction of a dozen independence leaders.
Clashes with police broke out in the Catalan regional capital late on Thursday when a mob of far-right anti-independence activists tried to storm a big separatist protest.
Health authorities in the region said 18 people were injured and the regional police arrested 11 protesters.
Spain’s central authorities said that 46 flights into and out of the region were cancelled on Friday due to a general strike called by pro-independence unions.
Picketers have also blocked the border with France at the major crossing point of La Jonquera.
Five marches of tens of thousands of people from inland towns are expected to converge in Barcelona’s centre on Friday afternoon for a mass protest with striking students and workers.