Pro-independence demonstrators and police clashed in Barcelona late on Saturday as protests that started the day peacefully turned violent.
At least six people were taken to hospital after officers charged on masked protesters and barricades were set alight.
Around 350,000 people rallied downtown earlier in protest at the jailing of nine separatist leaders for their role in a failed 2017 independence bid.
The turnout figure was given by the police as huge crowds packed into a wide avenue running between the waterfront and the city's Sagrada Familia basilica, which was again closed to visitors.
Barcelona has experienced daily pro-independence protests since October 14 when the Spanish Supreme Court sentenced the nine politicians and activists to up to 13 years in jail.
The situation began two years ago when the region staged a banned referendum on October 1 that was marred by police violence, then issued a short-lived declaration of independence, triggering Spain's worst political crisis in decades.
Saturday's rally was called by the ANC and Omnium Cultural, the region's two biggest grass roots pro-independence groups that have organised some of the largest separatist protests in recent years.
Marching down the spacious boulevard, demonstrators held up banners reading "We won't give in" and chanting "October 1, we won't forgive, we won't forget".
As a police helicopter passed overhead, they broke into loud boos and whistling.
"I feel really angry," said a 26-year-old computer technician from Tarragona called Marc, who did not give his surname. He described the heavy jail sentences handed to nine separatist leaders as "totally over the top, inhuman, and shameful".
"The violence doesn't sit well with me but it's normal to have a bit of upheaval like we've seen in Chile and Ecuador," he said of a wave of mass protests in Latin America.
"There are different ways of protesting but we have one objective: independence."
Catalans remain sharply divided over the question of separating from Spain, with a September poll showing 44 per cent in favour but 48.3 per cent against. The violent protests over the verdict have only deepened that division.
The violence declined last week although the protests continued, with thousands of students marching peacefully through Barcelona on Friday evening.
More than 600 people have been injured so far in the protests, among them 367 civilians, four of whom lost an eye, Catalan health officials say, with government figures showing 289 police were also hurt.
