Civil Guard riot police with shields used a hammer to smash the glass of the front door of the voting centre and lock cutters to force their way in.
Scuffles erupted outside between police and people waiting to vote at the centre in Sant Julia de Ramis, near the Catalan city of Girona.
Television footage showed police using batons to disperse the crowds gathered outside the local sports centre.
Catalan president Carles Puigdemont had been scheduled to vote there this morning. He has spearheaded the separatist politicians’ push to go ahead with the vote, despite a Constitutional Court suspension and fierce opposition by central authorities.
Parents, children and activists had occupied some of the 2,315 schools and other facilities to avoid them being closed by police acting on court orders.
Spain’s Constitutional Court ordered the vote to be suspended and central authorities say it is illegal.
Regional separatist leaders have pledged to hold it anyway, promising to declare independence if the “yes” side wins, and have called on 5.3 million eligible voters to cast ballots.