The general strike was organized by small unions of pro-independence workers and students. On paper, they are demanding improved social policies including a 35-hour work week and a higher minimum wage, but the protesters carried pro-secession flags and chanted slogans for the release of the 12 separatists currently on trial in the Madrid-based Supreme Court.
Regional police reported some clashes as strikers formed human chains to stop traffic on several highways across Catalonia, AP reported.
One protester was arrested for hitting an officer in downtown Barcelona, police said. Strikers, many of whom covered their faces, threw objects at a police line in a standoff on a rural highway before agents in riot gear advanced to disperse them. Protesters elsewhere burned tires on some highways.
Catalonia's transit authorities said the disruptions affected main thoroughfares in Barcelona and half a dozen major highways and railway tracks elsewhere in Catalonia.
The main unions in Catalonia did not back the strike.
In Barcelona, students and the pro-secession group ANC were planning separate marches later Thursday. ANC's protest slogan is "self-determination is not a crime." The Spanish government says regions cannot independently secede, according to the Constitution.
The trial into the roles played by the 12 separatists in Catalonia's failed 2017 secession attempt is in its second week. On Thursday, former Catalan government member Santi Vila and activists Jordi Sanchez and Jordi Cuixart are scheduled to testify at the court. The trial is expected to last for at least three months.
Election results and polls indicate that Catalonia's 7.5 million residents are equally divided over the secession issue.