Belgium’s prime minister, Charles Michel, was among the few national leaders to denounce the violence, which the Catalan government said had left 465 people injured as police forcibly removed voters from polling stations and on one occasion fired rubber bullets.
“Violence can never be the answer!” Michel said on Twitter. His Slovenian counterpart, Miro Cerar, also expressed his concern, saying he was “concerned” and calling for “political dialogue, rule of law and peaceful solutions”.
Former Belgian prime minister and senior MEP Guy Verhofstadt also said that while he did “not want to interfere” in Spain’s domestic affairs, “I absolutely condemn what happened today in Catalonia”. It was “high time for de-escalation,” he said.
In Britain, the prime minister, Theresa May, faced mounting calls to speak out against the scenes of police brutality in Catalonia after Labour, the SNP and the Liberal Democrats all criticised the Spanish government.
Human right groups also condemned the violence. Human Rights Watch said the state “has a duty to protect the rights to peaceful assembly and free expression” both of those opposed to independence and those who supported it.
Labour’s Jeremy Corbyn said the police violence against citizens was “shocking” and called on the Spanish government to “act to end it now”. Vince Cable, the Lib Dem leader, branded the police response “brutal and completely disproportionate”.
Nicola Sturgeon, the Scottish National party leader, also said she was concerned and that people “should be allowed to vote peacefully”. The vote is of particular interest in Scotland, which in 2014 voted in its own heated but largely peaceful independence referendum to remain in the the UK.
“Regardless of views on independence, we should all condemn the scenes being witnessed and call on Spain to change course before someone is seriously hurt,” Sturgeon said on Twitter.
A Foreign Office spokeswoman said: “The referendum is a matter for the Spanish government and people. We want to see Spanish law and the Spanish constitution respected and the rule of law upheld.”
Raül Romeva, Catalonia’s foreign minister, said on Sunday the pro-independence regional government had informed the EU of a “violation of fundamental rights that puts the very EU at risk”.
The bloc did not immediately respond to his demand that it “condemn the violence European citizens are suffering”. The referendum, which has been ruled illegal by Spain’s constitutional court, places the EU in a difficult position.
Romeva insisted last month that Brussels could no longer argue the vote was a domestic issue, but must “defend the Treaty of the European Union and stand for the general interest of Catalan citizens as the EU citizens that they are”.
Barcelona’s mayor, Ada Colau, who opposes independence but supports the right of Catalans to vote on the question, also called in an article in the Guardian for the EU to “defend the fundamental rights of Catalan citizens”.
But Jean-Claude Juncker, the European commission president, has said that Brussels must abide by the decisions of the Spanish government and of Spain’s constitutional court.
The commission has said on several occasions that a vote in favour of Catalan independence would be recognised but only if the referendum that produced it complied with the Spanish constitution and had been ruled legal.
Emily Thornberry, the shadow foreign secretary, said Labour believed debates on sovereignty “should be resolved in accordance with rules and laws” and any referendum “needs to be both democratic and fair”.
But it was “unacceptable for the Spanish authorities to overreact … through aggressive police action and the forcible closure of polling stations,” Thornberry said. “All sides must strive to come together and reach a political solution to this constitutional crisis.”
Video footage showed police hitting people in the crowd with batons while voters peacefully held up their hands, officers dragging women voters from polling stations by their hair, and Spanish police attacking Catalan firefighters.