As many as 337 people have been injured, some seriously, after Spanish police in riot gear cracked down on voters by firing rubber bullets and stormed polling stations to confiscate ballot boxes to halt the Catalonia independence referendum.
But, Catalans managed to cast their ballots in the poll, which the Spanish authorities have declared illegal.
The voting has been marred by a brutal police crackdown in which several instances of violence against voters have been recorded and in some places ballot boxes were forcibly seized by the Spanish police.
Catalonia's pro-independence regional government has pressed ahead with the referendum despite implacable opposition from the Spanish state.
Nine police officers and two members of the Guardia Civil have been injured in the melee, the Guardian quoted the Spanish interior ministry as stating.
There have been several calls from Catalan politicians and opposition MPs for Spanish Prime Minister Mariano Rajoy to resign over the police response.
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Barcelona's mayor Ada Colau has called on Spanish Prime Minister to resign amid the Catalonia's independence referendum which begun today with clashes occurring as police attempted to prevent voting from taking place.
The mayor also demanded that police must stop using violence against voters.
The Spanish government considers the referendum unconstitutional and had ordered the police to seal public facilities to prevent voting.
Videos show police dragging voters from polling stations by their hair, unprovoked attacks on protesters and Spanish police attacking Catalan firefighters.
Human Rights Watch has released a statement calling on Spanish authorities to respect their citizens' right to peaceful assembly and refrain from using excessive force.
The regional government spokesperson Jordi Turull has accused Rajoy of being responsible for "a state violence unknown to Spain since the age of Franco," referring to the former military dictator Francisco Franco who ruled the country with an iron fist for 36 years until 1975, the local media reported .