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Violent clashes have erupted between police and protesters for the second day in a row over the conviction of 12 Catalan separatist leaders.

Thousands of people held vigils on Tuesday near the Spanish government offices in Catalonia's four provinces.

However it was in the northeastern regional capital, Barcelona, where police charged at protesters after some hurled firecrackers and other objects at officers and kicked temporary fences put in place to protect the building.

The protesters sang the Catalan anthem and shouted "the streets will always be ours," "independence," as well as slogans calling Spanish police "occupying forces" and urging them to leave Catalonia.

They erected improvised barricades with trash bins, fences, and piles of cardboard that they set on fire.

The evening vigils, also in Girona, Lleida and Tarragona, as well as smaller towns across Catalonia, had been called by ANC and Omnium, two grassroots pro-secession groups whose leaders Jordi Sanchez and Jordi Cuixart were sentenced on Monday to nine years in prison for sedition.

Seven politicians were also given prison terms of around a decade in Monday's landmark Supreme Court ruling.

Three more were fined for disobeying the laws as they pushed ahead with a banned referendum on October 1, 2017, and briefly declared independence based on its results before Spain crushed the defiance.

Activists also blocked highways, smaller roads and railway tracks for brief periods on Tuesday, following an attempt to besiege Barcelona's international airport the night before that left thousands of passengers stranded.

Many, desperate to catch their flights, were forced to walk with their luggage on highways and across fields.

Authorities said that three people were arrested and more than 170 others injured in Monday's protests, including about 40 police officers and a protester who lost an eye.

The airport authority said that 110 flights were cancelled on Monday and 45 on Tuesday. Nearly 1,000 were operating normally, AENA said.

Most impromptu protests are responding to an online campaign by Tsunami Democratic - a loose, leaderless grassroots group that uses encrypted messaging apps to call for peaceful disobedience.

Spain's caretaker interior minister, Fernando Grande-Marlaska, said that authorities were investigating the group.

Considered a traitor by the pro-independence camp, Vila resigned as Catalonia's business minister a day before the Catalan Parliament unilaterally declared secession on October 27, 2017.

Protests are likely to extend throughout the week. A three-day student strike begins Wednesday in the region, and a worker's union has called a separate strike for Friday.