Thousands of people are protesting in Barcelona to demand the release of two Catalan pro-independence activists jailed by Spanish authorities in a sedition case.
The demonstrators have flooded a main avenue, holding up candles, pro-independence "estelada" flags and chanted "political prisoners, freedom".
The jailed activists are Jordi Sanchez and Jordi Cuixart, who lead two different grassroots groups.
On Monday, a Madrid judge provisionally jailed Sanchez and Cuixart in a sedition investigation.
The judge ruled they were behind huge demonstrations on September 20 and 21 in Barcelona that hindered the police operation against preparations for an October 1 independence referendum.
On Tuesday Spain's top court ruled that the referendum was unconstitutional, adding legal weight to the government's efforts to block an attempt by the region to break away from Spain.
The Constitutional Court's ruling was not a surprise, with the Spanish government repeatedly insisting the referendum was illegal.
"We are facing an executive power in the state that uses the judiciary branch to block the legislative," Catalan government spokesman Jordi Turull told reporters shortly after the Constitutional Court ruling was announced.
Catalan President Carles Puigdemont made an ambiguous statement about the region's future last week, saying he has the mandate to declare independence but adding that he would not immediately move to implement it in order to allow time for talks with the central government.
Spain has said that no dialogue can take place with independence on the table because a reform of the country's Constitution with an ample majority in the national parliament is the only legal way to achieve secession.