Catalonia today announced a law to make formal its plans for an October 1 referendum on whether to declare independence from Spain, a vote the government says is illegal and has said it will stop.

Catalan lawmakers are due to vote later today on the referendum law and the legal framework needed to set up an independent state. The laws will likely be approved because pro-independence parties have a majority in the regional parliament.

Polls in the northeastern region, whose capital is Barcelona, show support for self-rule waning as Spain's economy improves. But the majority of Catalans do want the opportunity to vote on whether to split from Spain.

Polls in the northeastern region, whose capital is Barcelona, show support for self-rule waning as Spain's economy improves.

The government today said it had asked the Spanish constitutional court to declare the referendum law void as soon as it approved by the regional parliament. The Spanish constitution states that the country is indivisible.

"What is happening in the Catalan parliament is embarrassing, it's shameful," Deputy Prime Minister Soraya Saenz de Santamaria told reporters.

The details of the referendum, which aims to pose the question "Do you want Catalonia to be an independent republic?" to all Spanish citizens living in Catalonia, were revealed amid a tense atmosphere in the regional parliament.

"Be very clear that you will not split up Spain, but you are breaking up Catalonia," Alejandro Fernandez of the ruling People's Party (PP) told pro-independence lawmakers. "You're putting social harmony at risk."

Be very clear that you will not split up Spain, but you are breaking up Catalonia

There will be no minimum turnout requirement to make the result of the vote binding, regional government head Carles Puigdemont said in a recent briefing. Ballot boxes, voting papers and an electoral census are at the ready, he said.

Under the terms of the new laws, the Catalan parliament will declare independence within 48 hours of a 'yes' vote.

Spanish Prime Minister Mariano Rajoy told a news conference on Monday the government would come down with all the force of the law to ensure no referendum would go ahead on October 1.

Courts have already suspended from office and leveled millions of euros in fines at Catalan politicians who organised a non-binding referendum in 2014, which returned a "yes" vote on a low turnout.