Barcelona: Mass protests broke out across Spain's Catalonia region after its former separatist leader Carles Puigdemont was arrested in Germany, media reports said.

The former Catalonian regional president's lawyer said he was being held at a police station in Neumunster, Germany and was arrested on Sunday as he was returning from Finland to Belgium, the country he fled to in October after the Spanish judiciary announced it would be investigating him for his alleged part in organising a separatist referendum and the subsequent declaration of independence.

A spokesperson for the Kiel city criminal police told Efe news that Puigdemont was picked up at 11.19 a.m., on a road that connects Germany and Denmark.

Judicial sources have said that Germany now has up to 90 days to decide whether to extradite Puigdemont to Spain, a move to which he is opposed as he believes he would not get a fair trial there.

Puigdemont will appear before a German judge on Monday.

The biggest protest took place in Barcelona where over 55,000 pro-independence protesters took to the streets on Sunday night, carrying Catalonian flags and banners with slogans emblazoned across them, reports CNN.

Footage posted on social media shows crowds meeting with police wearing helmets, but the protests appeared to be peaceful.

A spokesman for the regional police force, the Mossos d'Esquadra, said four people were arrested during the demonstrations, and the Catalan Emergency Services said about 50 people received medical attention for mild injuries.

Smaller demonstrations were held in Girona, where Puigdemont once served as mayor, Tarragona and Lleida. Some protesters also formed road blocks in various locations, the BBC reported.

Tensions in Catalonia are very high and its separatist leaders abandoned plans to name a new President after the arrest on Friday of the latest candidate, Jordi Turull.

Spain's Supreme Court has ruled 25 that Catalan leaders should be tried for rebellion, embezzlement or disobeying the state. They all have denied the allegations.

The charges Puigdemont faces in Spain could result in up to 30 years in prison.