Violence breaks out in Cataloni during the vote, police break into... (Photo/Video)

The Spanish government has pledged to ban a vote that was declared illegal by the country's constitutional court writes BBC broadcasts Periscopi.

The interior ministry says police officers began catching ballot sheets and boxes when polls opened.

The riot police, like the Catalans, call it blocking potential voters to enter a polling station in Barcelona's regional capital and use violence against them.

Major crowds have gathered outside the polling stations in Catalonia to vote in the Spanish government-opposed independence referendum.

Catalan government officials said the ballot boxes have been opened and have predicted a strong turnout.

Police are also confiscating voting papers, while prosecutors have ordered closure of voting-related websites and the arrest of officials who are organising the referendum. Yet, Catalan leader Charles Puigdemont told Reuters they would not stop.

Why is their vote valid?

Catalonia, a rich region of 7.5 million people in northeastern Spain, has its own language and culture.

It also has a high degree of autonomy, but is not recognised as a particular nation under the Spanish Constitution. /Periscopi/