Catalonia's executive admitted Thursday that plans for an outlawed independence referendum had been dealt a major blow by a police crackdown, but vowed to press ahead, urging support from the global community.
Visitors to Barcelona are being warned of demonstrations in the city that could disrupt travel.
The students are carrying pro-independence flags and banners supporting the October 1 vote.
Civil Guard police this week arrested around a dozen regional government officials and seized about 10 million ballot papers.
The ministry said the Catalan Interior Ministry had been informed.
Spain will deploy police reinforcements to Catalonia if an independence referendum pledged by Catalan officials but opposed by the national government goes ahead, officials have said.
Many who do not support independence say they are scared to speak out and no longer feel comfortable in their own country.
Authorities in the wealthy north-eastern region insist the vote will take place, even though Spain's Constitutional Court has ordered it to be suspended and the Madrid-based national government insists it is illegal. Three ferries docked at Barcelona's port will provide accommodation for the extra officers. But Prime Minister Theresa May has ruled out it out for now, saying the United Kingdom needed certainty, stability, and strong leadership following last year's referendum, in which 52 percent of Britons voted leave the EU.
A pro-independence group said about 2,500 supporters were at the protest in Hospitalet.
The protesters gathered outside the High Court demanding that the leaders be freed, while a Catalan government spokesman said eight of the 14 people arrested had been released. Spain's Constitutional Court said September 21 it will begin fining 22 electoral board members appointed to oversee Catalonia's planned independence referendum between $7,200 and $14,400 a day as long as they fail to comply with a court order suspending the ballot.