There were scenes of calm inside, despite the clashes witnessed outside some of Catalonia’s polling stations.
Queues numbering hundreds of people were lined up throughout the region to respond to the question:
“Do you want Catalonia to become an independent state in the form of a republic?"
Madrid says the ballot defies the 1978 constitution.
Legal or not, the ‘yes’ vote is likely to win as most of those in favour of independence said they would go to the ballot box, while those against said they would not take part.
Around 70 polling stations were raided by police, according to Spain’s Interior Minister, Juan Ignacio Zoido.