Supporters of Catalan independence have begun occupying polling stations in a bid to protect Sunday’s vote from a crackdown by the Spanish government.

The vice-president of Spain’s secessionist north-eastern region warned that backers of Catalonia’s independence would cast their ballots even if national police “took voting stations by assault”.

Politicians in Catalonia have insisted the referendum will go ahead, despite Madrid attempting to shut down what they said was an illegal poll.

Catalan authorities said the majority of eligible voters were expected to take part, and they would declare independence within 48 hours after announcing the vote's results, if the yes side wins.

Madrid's culture minister Inigo Mendez de Vigo, acting as a spokesman for Spain's cabinet, accused the secessionist coalition ruling Catalonia of bending the laws to go ahead with a vote regardless of warnings from courts and a suspension by the country's Constitutional Court earlier this month.

The Spanish government has fought the referendum with a myriad of legal actions, and last week the Guarda Civil stormed Catalan regional government buildings.

"The government has a constitutional mandate to enforce the laws maintaining civic order," Mr Mendez de Vigo said.

"Nobody is above the laws and whoever violates them will face consequences."

Catalonia referendum protests – in pictures Show all 10 1 /10 Catalonia referendum protests – in pictures Catalonia referendum protests – in pictures Demonstrators block a Guardia Civil vehicle as they try to leave the Department of External Affairs, Institutional Relations and Transparency of the Catalan Government office in Barcelona AP/Emilio Morenatti Catalonia referendum protests – in pictures Demonstrators react as they try to stop the car carrying Xavier Puig, a senior at the Department of External Affairs, Institutional Relations and Transparency of the Catalan Government office, after he was arrested by Guardia Civil officers in Barcelona AP/Emilio Morenatti Catalonia referendum protests – in pictures A demonstrator reacts as he tries with others to stop the car carrying Xavier Puig, a senior at the Department of External Affairs, Institutional Relations and Transparency of the Catalan Government office, after he was arrested by Guardia Civil officers in Barcelona AP/Emilio Morenatti Catalonia referendum protests – in pictures Spokeswoman of the Catalan pro-independence anticapitalist party "Candidatura d'Unitat Popular - CUP" (Popular Unity Candidacy), Ana Gabriel, talks to the media in Barcelona Josep Lago/AFP Catalonia referendum protests – in pictures Republican Left of Catalonia party's (ERC) Member of Parliament Joan Tarda (C) attends a demonstration outside the regional Economy Ministry in Catalonia during a police search for documents connected with the organisation of the Catalan independence referendum, in Barcelona EPA/Alejandro Garcia Catalonia referendum protests – in pictures A man holds pro-referendum poster next to a Spanish Civil Guard who stands in front of the Economy headquarters of Catalonia's regional government in Barcelona. The operation comes amid mounting tensions as Catalan leaders press ahead with preparations for an independence referendum on October 1 despite Madrid's ban and a court ruling deeming it illegal Josep Lago/AFP Catalonia referendum protests – in pictures People hold placards reading "Democracy" as they protest in front of the Economy headquarters of Catalonia's regional government in Barcelona AFP Catalonia referendum protests – in pictures A crowd of protesters gather outside the Catalan region's economy ministry after junior economy minister Josep Maria Jove was arrested by Spanish police during a raid on several government offices, in Barcelona Reuters/Albert Gea Catalonia referendum protests – in pictures People holding 'Esteladas' (Catalan pro-independence flags) attend a protest near the Economy headquarters of Catalonia's regional government Lluis Gene/AFP Catalonia referendum protests – in pictures People demonstrate on a Spanish Civil Guard Police car outside the Catalan Vice-President and Economy office as police officers holds a searching operation inside David Ramos/Getty Images

However, Catalonia's vice-president, Oriol Junqueras, said Catalan citizens will be able to vote "even if somebody takes voting stations by assault and tries to avoid something as natural as placing a voting slip in a ballot".

Reports from the AFP news agency that Catalans were occupying polling stations to protect the referendum followed a warning from Spanish police that they would take control of voting booths to help thwart the planned independence vote.

Spain's constitution says only the nation's government can call a referendum on sovereignty.

Police forces acting on judges' orders have seized ballots and arrested regional officials in the crackdown.

Mr Junqueras said an internal poll showed more than 60 per cent of the 5.3 million eligible voters plan to cast ballots.

He displayed a prototype of the plastic ballot boxes planned for more than 2,300 voting stations.

A senior European official, meanwhile, said any moves "should be done in accordance with the constitution of that member state".

European Commission vice-president Frans Timmermans said: "That is the rule of law, you abide by the law and the constitution even if you don't like it."

In Madrid, a Spanish conservative group set up a large, mock ballot box in the centre of the city and urged people to vote whether they want Catalonia to remain part of Spain.