Masked protesters confronted officers near the national police headquarters in Barcelona late on Friday, throwing stones and cans at lines of officers in riot gear. Rubbish bins were dragged into the streets and set alight.
Police responded with tear gas, rubber bullets and water cannon, reports said.
Further north, Catalan police closed the motorway at La Jonquera on the French border as about 200 protesters occupied the road. Demonstrators blocked at least 20 major roads across the region, reports said.
Fresh clashes between riot police and protesters have broken out in Barcelona amid anger over the jailing of Catalan separatist leaders.
A general strike was announced and five huge marches, all peaceful, converged on the city centre, bringing the streets to a standstill.
Police estimated that more than 500,000 people joined Friday’s rallies. Protesters also blocked a motorway on the Spain-France border, causing huge tailbacks.
There were 17 arrests across the region on Friday, Spanish newspaper El Pais reported, and 62 people were injured – 41 of them in Barcelona. At least 96 people were hurt as the protests spread across Spain’s north-eastern region.
Catalan regional leader Quim Torra thanked those who had demonstrated peacefully and criticized the rioters.
He said the sentences handed down to separatist leaders would not deter the campaign for independence.
“We’ll return to the ballot box again on self-determination,” he said. Speaking in Brussels, acting Spanish Prime Minster Pedro Sanchez warned that those who caused disturbances would face justice.
“There is no space for impunity in relation to the serious acts of violence we have witnessed over recent days in different cities in Catalonia,” he said.
Fernando Grande-Marlaska, Spain’s acting interior minister, said there had been nearly 130 arrests since trouble broke out across Catalonia five days ago. He warned that rioters faced up to six years in prison.
The separatists were convicted of sedition over their role in a 2017 referendum outlawed by the Spanish courts and a subsequent declaration of independence. Another three were found guilty of disobedience and fined but not jailed. All 12 defendants denied the charges.
Former Catalan President Carles Puigdemont is still wanted by the Spanish authorities for his role in the referendum. He currently resides in Belgium. If he returns to Spain, he will be arrested.
What is behind the Catalonia unrest?
Catalan nationalists have long complained that their region, which has a distinct history dating back almost 1,000 years, sends too much money to poorer parts of Spain via taxes which are controlled by Madrid.
The wealthy region is home to about 7.5 million people, with their own language, parliament, flag and anthem.
In September, a march in Barcelona in support of Catalonia’s independence from Spain drew crowds of about 600,000 people – one of the lowest turnouts in the eight-year history of the annual rally.