(bbc) -- Catalonia's independence referendum has begun in chaotic fashion, with police attempting to prevent the vote from taking place.

The Spanish government has pledged to stop a poll that was declared illegal by the country's constitutional court.

Police officers are blocking potential voters from entering polling stations, and are also seizing ballot papers and boxes.

Nonetheless, Catalan government officials have predicted a big turnout.

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.

Ahead of the polls opening, the Catalan government said voters could use any polling station if their designated voting place was shut.

(Photo: Riot police moved in on polling stations as the time came for them to open, AFP)