Protesters blocked roads and train lines across Catalonia on Wednesday, provoking commuter anger in a strike called by a pro-independence union after separatist leaders were detained in Madrid over their divisive secession drive.
Roads and major motorways were cut in about 60 places, causing widespread disruption in the region, which has been plunged into uncertainty over its now-deposed government's bid to split from Spain.
But by early afternoon, the protests had eased, with only around six blockages remaining in the region, an interior ministry official said.
The independence crisis has shaken a European Union still getting to grips with Britain's decision to leave the bloc, and raised fears of social unrest and prolonged disruption to the eurozone's fourth-largest economy.
On Wednesday, Spain's Constitutional Court struck down the declaration of independence made by Catalan lawmakers on October 27 -- which led Madrid to dismiss the government and assume control of the region -- declaring it "unconstitutional and void."
Madrid is organising new regional elections for next month as it tries to stem the fallout from Spain's deepest political crisis in decades.
- 'Coup d'etat' -
Huge banners were draped across at least one tunnel in Barcelona, blocking entry, and activists also cut off main roads linking the region of 7.5 million people to France and to the Spanish capital.
At one protest in Sitges, southwest of Barcelona, demonstrators set up banners, deckchairs and a table-top game of chess as long queues of motorists formed.
But despite the disruptions, the work stoppage was smaller than during a general strike on October 3 that followed a banned independence referendum, in which 90 percent voted to break from Spain.
During that strike most shops and tourist attractions closed down in Barcelona while they remained open on Wednesday, though activists blocked access to the Sagrada Familia basilica.
Juan Antonio Puigserver, an interior ministry official, said participation in Wednesday's strike had been "minimal" in most sectors, except in education where it reached 31.5 percent.
A judge in Madrid last week ordered eight separatist politicians to be remanded in custody over their secession drive.
Deposed Catalan leader Carles Puigdemont, who fled to Belgium where he is facing extradition to Spain, on Tuesday criticised the EU for backing Prime Minister Mariano Rajoy in the crisis.
"Will you accept the result of the Catalan referendum or will you continue to help Mr Rajoy in his coup d'etat?" Puigdemont said in Brussels.
Belgian Prime Minister Charles Michel on Wednesday denied that his government was "in crisis" over Puigdemont's presence, after Flemish separatist members of his coalition government spoke out in support of Catalan independence.
He added that Puigdemont's presence in Belgium was a "matter for the courts, not for the government."
Rajoy responded by tweeting: "We must respect the rule of law and therefore the independence of Belgian and Spanish judges."
- Tensions flare -
More than 2,000 businesses have moved their headquarters out of the region as the turmoil drags on.
Wednesday's walkout was called by the pro-independence CSC union but lacked support from Spain's two largest unions.
Waving pro-independence banners and Catalan flags, demonstrators called for the release of sacked government officials and separatist lobbyists.
In Barcelona, several thousand gathered outside the Catalan government building, some holding banners reading: "This isn't justice, it's dictatorship".
Authorities said high-speed train links with France were disrupted, with a Barcelona-Lyon train forced to turn back, but commuter trains were running as normal by midday (1100 GMT).
New elections will be held in Catalonia on December 21 and Rajoy called on Wednesday for "massive participation" in the vote.
Puigdemont has called for a united separatist front to participate, but a former government ally, the leftwing ERC party, on Tuesday ruled out running on the same ticket.