Catalonia’s disputed independence vote has quickly descended into chaos on Sunday as Spanish national police entered polling stations, seizing ballot boxes and voting papers, the media reported.

In the town of Girona, where the regional President Carles Puigdemont was due to vote, the police smashed their way into a polling station by breaking a glass window, reports CNN.

“Police are confiscating ballot boxes to respect the judicial mandate and the law regarding the illegal referendum,” Spain’s Interior Ministry tweeted.

The Spanish government has pledged to stop the vote that was declared illegal by the country’s constitutional court.

The ballot papers contain just one question: “Do you want Catalonia to become an independent state in the form of a republic?” There are two boxes: Yes or No.

Meanwhile in Barcelona, lines of Guardia Civil attempted to prevent voters from entering polling stations.

In the run-up to the vote, national authorities have seized ballot papers, voter lists and campaign material, as well as sending thousands of extra police, or Guardia Civil, to the region.

High-ranking Catalan officials involved in organizing the referendum have also been arrested.

In the past few days, authorities blocked the use of a voting location app and seized vote-counting software, CNN reported.

Puigdemont, who called the referendum in June, had urged voters to go to the polls Sunday despite Madrid’s opposition.

The Catalan government tweeted on Friday that 2,315 polling stations would be open for the referendum, with more than 5.3 million voters on the electoral roll.

Polling stations were due to open at 9 a.m. and close at 8 p.m., Joan Maria Pique, the international communications director for the Catalonian government told CNN.

Results are expected around 10 p.m.

Most of the polling stations are in schools, where parents and teachers have organised activities for families over the weekend.

Catalonia, a wealthy region 7.5 million people in north-eastern Spain, has its own regional government, or Generalitat, which already has considerable powers over healthcare, education and tax collection, but is not recognised as a separate nation under the Spanish constitution.

Catalonia’s campaign to break away from Spain has gained momentum since 2010, when Spain’s economy plunged during the financial crisis.

Catalonia held a symbolic poll in 2014, in which 80 per cent of voters backed complete secession — but only 32 per cent of the electorate turned out.