Voting began on Sunday for the Catalan regional government's independence referendum in an attempt to break away from Spain, the media reported.
The Spanish government has pledged to stop the vote that was declared illegal by the country's constitutional court, reports the BBC.
The ballot papers contain just one question: "Do you want Catalonia to become an independent state in the form of a republic?" There are two boxes: Yes or No.
The officers then began seizing ballot papers and boxes as the polls opened at 9 am (local time).
Thousands of separatist supporters occupied schools and other buildings that have been designated as voting centres ahead of the polls opening.
In some areas, farmers positioned tractors on roads and in front of polling station doors, and school gates were taken away to make it harder for the authorities to seal buildings off.
Referendum organisers have called for peaceful resistance to any police action, the BBC reported.
Catalan government officials have predicted a big turnout.
Civil guards clear people away from the entrance of a sports center, assigned to be a polling station by the Catalan government and where Catalan President Carles Puigdemont is expected to vote near Girona, Spain. (Photo: PTI)Sunday would be an "important date for democracy", regional Vice-President Oriol Junqueras told TV3, the main Catalan public channel on Saturday.
Catalonia, a wealthy region of 7.5 million people in north-eastern Spain, has its own language and culture.
It also has a high degree of autonomy but is not recognised as a separate nation under the Spanish constitution.
Television footage showed helmeted, armed police breaking the glass of the entrance door and walking into the sports centre, which had been designated as a polling station.