Dozens of people have been hurt as Spanish police tried to stop millions of people voting in a referendum on independence in the region of Catalonia.
Rubber bullets were fired in Barcelona, the region's capital, and police seized ballot boxes and smashed their way in to polling stations.
Catalan emergency services said 38 people were hurt, mostly with minor injuries, as a result of police action.
Eleven police officers were also hurt.
Reports said people were forcibly removed from polling stations by baton-wielding police.
Catalan regional leader Carles Puigdemont accused Spanish authorities of using "unjustified, disproportionate and irresponsible" violence in a crackdown on a Catalan independence referendum on Sunday.
The batons, rubber bullets and violence used by Spanish police to prevent voting in what Spanish authorities have said was an illegal referendum had shown a "dreadful external image of Spain", he added.
Electoral volunteers said they were unable to access census data because web services to polling stations had been cut, providing an obstacle to the casting of votes.
Guillem Castillo, an 18-year-old engineering student volunteering as an electoral official at a Barcelona high school, said technical problems halted the voting shortly after it opened.
Spanish media reported similar problems with internet in polling centres across Catalonia.
Voting was still going ahead at the polling stations lacking internet as people could still vote by paper.
Many people took to social media to condemn the loss of internet and access to the census websites, including Julian Assange.
More than five million people have been invited to take part in the independence referendum by the regional Catalan government despite it being deemed 'illegal' by the Spanish central government and courts.
The ballot papers contain one question: "Do you want Catalonia to become an independent state in the form of a republic?" with two boxes: Yes or No.
Regional separatist leaders have promised to declare independence if the "yes" side wins, and have called on all 5.3 million eligible voters to cast ballots.
The Spanish government's top official in Catalonia says that security forces were acting "professionally" to enforce a judicial decision to halt a banned referendum on the region's secession from Spain.
Enric Millo, the central government's delegate in the northeastern region, has thanked the National Police and Civil Guard forces for their efforts to "oversee safety of all Catalans and for guaranteeing their rights."
Mr Millo said that "today's events in Catalonia can never be portrayed as a referendum or anything similar."
Agencies contributed to this report
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