German police arrested Puigdemont earlier on Sunday as he crossed over by auto from Denmark, where had been visiting lawmakers.
Puigdemont's arrest is the latest chapter in a secession saga that has bitterly divided Catalans and triggered Spain's worst political crisis in decades.
The decision ended Puigdemont's hopes of again taking up the post, because he refused to return to Spain due to the sedition and rebellion charges awaiting him there. He was in Finland at the time, promoting the cause of independence for Catalan.
Police dressed in riot gear are struck demonstrators with batons as they tried to push back a large crowd that wanted to advance on the office of the Spanish government's representative in Catalonia. Puigdemont had made clear his preference to fight the extradition process from Belgium.
"The president was going to Belgium to put himself, as always, at the disposal of Belgian justice", Pique told Reuters.
Spanish police said the arrest came thanks to a "coordinated operation between police and the CNI", Spain's intelligence agency.
Germany now has 60 days to determine whether to extradite Puigdemont to Spain.
Elsa Artadi, a member of the Catalan parliament considered to be in Mr Puigdemont's inner circle, wrote on Twitter: "Spain does not guarantee a fair trial, only revenge and repression".
The ex-leader is being sought by Spanish authorities on charges of rebellion, after he led his separatist movement in a bid for an independent Catalonia. "Trying to destroy a European democracy, bypassing democratic laws, breaking up coexistence or misusing public money can not enjoy impunity".
Puigdemont had hoped to again be elected president of Catalonia in December, when separatists won a new vote in the region, which Madrid had called for after dissolving the regional government.
Mr Puigdemont was en route from Finland to Belgium, his self-imposed home-in-exile for the last five months, when he was detained shortly after 11am at an Autobahn petrol station near the northern town of Schleswig.
Finland's National Bureau of Investigation (NBI) confirmed on Saturday it had received a European arrest warrant for "a Spanish citizen visiting Finland".