More than 5.3 million people have been called upon to have their say on independence from Spain in the wealthy northeastern region which has its own distinct language and culture.

The referendum poses the question: “Do you want Catalonia to become an independent state in the form of a republic?”

But it has been ruled unconstitutional by the central government in Madrid and the courts, with judicial officials ordering police to seize ballot papers, detain key organisers and shut down websites promoting the vote.

Thousands of Spanish police fanned out across the region on Sunday, forcing their way into polling stations.

In central Barcelona, riot police charged at demonstrators who were sitting on the ground blocking their way after they raided a polling station at a school, witnesses said.

They also said police had fired rubber bullets.

The crackdown drew a sharp rebuke from Catalan leaders.

“The unjustified use of violence, which is both irrational and irresponsible, by the Spanish state will not stop the will of the Catalan people,” Catalan leader Carles Puigdemont said.

The police, he said, used “batons, rubber bullets and indiscriminate force” against people wanting to vote “peacefully”.

Riot police also stormed a polling station near Girona, smashing the glass doors of the sports centre where Puigdemont was expected to vote.

But the regional government said Puigdemont managed to vote anyway, tweeting pictures of him casting his ballot in Cornella del Terri, 10km away.

The drama unfolded after a night of tension in which thousands of people, both nervous and excited, gathered outside polling stations before dawn, joining those who had spent the night camping inside to ensure they would be open on the day.

Under a sea of umbrellas outside a school in Barcelona, a mixed crowd of people gathered to vote, among them elderly people in wheelchairs, families with buggies and parents clutching toddlers by the hand. With no police in sight, they were able to cast their ballots, prompting scenes of jubilation.

“I’ve voted! I’ve voted,” one man shouted.

“That’s the great hope, to be able to vote freely like this despite the problems we’ve faced, I’m very happy. I can die peacefully,” added Jose Mas Ribas, 79.

Elsewhere in Barcelona, rows of police vans lined the streets, their blue lights flashing as officers in riot gear, some carrying heavy bolt cutters, walked past crowds massed outside another polling station.

“We will vote!” they chanted, many with their hands in the air.

Although Catalans are divided over independence, most want to vote on the matter in legal, binding plebiscite.

The Spanish government’s representative in Catalonia placed the blame for the chaos on the regional leadership.

“Puigdemont and his team are solely responsible for all that has happened today and for all that can happen if they do not put an end to this farce,” Enric Millo told a news conference.

“The sole objective of today’s operation has been to ensure that this illegal referendum does not take place and the Spanish and Catalan people can continue to live in peace and liberty as they have these past 40 years.”

Pro-separatist lawmakers in Catalonia have pushed for an independence referendum since September 2015 when they won a narrow majority of 72 seats in the region’s parliament.

Although Catalonia already has significant control over education, health care and welfare, the region says it pays more in taxes than it receives in investments and transfers from Madrid.

This has sparked resentment which has been further exacerbated by Spain’s economic doldrums.

The Catalan government says independence would leave the region richer and more able to protect its language and culture

Whatever happens, the result will not be recognised by Madrid, and almost certainly not by the international community.

The referendum law foresees a declaration of independence within 48 hours of a ‘yes’ vote. But it is unclear what the regional government will actually do so.

If nothing else, the conservative government of Prime Minister Mariano Rajoy has come under fire for limiting its response to the crisis to repeating that the referendum is unconstitutional.

“The state needs to explain the benefits of remaining united, instead of repeating all the time that the referendum is illegal,” said Rafael Castillo, a 59-year-old engineer at a rally in Madrid, wearing a scarf with the Spanish flag around his neck.

Additional reporting by Associated Press