Spanish Prime Minister Mariano Rajoy vowed Thursday to take legal action to block an independence referendum in Catalonia which he branded an "intolerable act of disobedience".

Rajoy gathered his cabinet for an emergency meeting to formally ask Spain's Constitutional Court to once again rule against the plebiscite called for October 1.

He also said all 947 mayors in Catalonia would be warned over their "obligation to impede or paralyse" efforts to carry out the vote which he said is unconstitutional.

"This referendum, no matter how much they try to impose it in a hasty, amateur and illegal way, will not take place," Rajoy said.

Catalonia's regional parliament, which is controlled by separatists, voted Wednesday to push ahead with the referendum in the wealthy northeastern region, sparking the country's deepest political crisis in 40 years.

Spain's top prosecutor meanwhile said voting materials would be seized and "criminal charges are being prepared" against the leaders of the Catalan parliament as well as officials in the regional government who prepared the referendum decree.

General prosecutor Jose Manuel Maza told reporters the officials could be charged, among other things, with disobedience, abuse of power and embezzlement.

Maza added that regional prosecutors with the aid of police had been told to investigate any actions taken to organise the vote.

'Covert state of siege'

The warnings were brushed aside by a Catalan government spokesman, who insisted the referendum would take place despite a "covert state of siege" being imposed by the central government in Madrid.

"This does nothing to alter the government's project," Jordi Turull said. "Faced with this covert state of siege, we now feel obliged to defend our most fundamental rights."

Catalonia's president Carles Puigdemont, a lifelong proponent on independence, is hoping to mobilise supporters in a show of legitimacy in the face of Madrid's threats to halt the vote by any means possible.

He sent a letter to Catalonia's mayors on Thursday asking them to give notice within 48 hours of what locations they could make available for ballot stations.

The Catalan government also began to recruit volunteers through its web page to help stage the referendum.

Ada Colau, the mayor of Barcelona, the capital of Catalonia where separatists are a minority, would not say if she would allow ballot stations to be set up on municipal property.

In a Twitter message she said only that she is always ready "to facilitate participation in all democratic mobilisations, without putting at risk institutions or public workers".

Catalonia accounts for about one-fifth of Spain's economic output, and already has significant powers over matters such as education and healthcare.

But Spain's economic worries, coupled with a perception that the region pays more in taxes than it receives in investments and transfers from Madrid, have helped push the cause of secession from the fringes of Catalan politics to centre stage.

Adding to the rise in separatist sentiment was a 2010 ruling by the Constitutional Court striking down parts of a 2006 autonomy charter which granted new powers to Catalonia and recognised it as "a nation".

'Won't be recognised'

Opinion polls show that Catalans are evenly divided on independence. But over 70 percent want a referendum to take place to settle the matter, similar to the plebiscite held in Scotland in 2014.

The president of the European Parliament, Antonio Tajani, warned that an independent Catalonia would be left outside of the European Union.

Caroline Gray, an expert on Spanish independence movements at Britain's Aston University, said the referendum would lack legitimacy if it goes ahead since people who oppose independence would likely stay home just as they did during a mock referendum in 2014.

Over 80 percent of participants voted to split from Spain during that symbolic plebiscite -- though only 2.3 million of Catalonia's 5.4 million eligible voters took part.

"If we look at it from how Spain and the international community is going to react, I think it is difficult to see how people will take it more seriously than previous attempts which did not work," Gray told AFP.

"It would be very difficult for the Catalan government to get to the stage to be able to proclaim independence because it won't be recognised beyond its own authorities."