Prime Minister Mariano Rajoy will chair an emergency cabinet meeting in response to Catalan leader Carles Puigdemont's announcement yesterday that he had accepted "the mandate of the people for Catalonia to become an independent republic" following a banned referendum earlier this month.
But Puigdemont in his declaration to parliament called for Catalonia's independence to be suspended to allow for negotiations with Madrid.
Rajoy has vowed to use everything in his power to prevent independence and has refused to rule out imposing direct rule over the semi-autonomous region -- an unprecedented move many fear could lead to unrest.
Crowds of thousands gathered outside the parliament building in Barcelona last evening, waving Catalan flags and banners screaming "democracy" in the hope of witnessing a historic night in a region that remains deeply divided over independence.
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But Spain's political establishment rounded on Puigdemont following the declaration, and support among separatists in Catalonia was mixed.
Deputy prime minister Soraya Saenz de Santamaria told reporters shortly after the signing that Puigdemont was "a person who doesn't know where he is, where he's going or with whom he wants to go".
"I find it even worse because it is suffering a longer agony. Indecision and uncertainty is the worst thing that can happen to us," she told AFP.
Political leaders in Catalonia, Spain and Europe have come out against secession, concerned over the country's biggest upheaval in decades.
Following his declaration to parliament, Puigdemont and his allies signed an independence declaration outside the chamber, but its legal validity was unclear.
Spain and Catalonia now enter into the unknown, as Madrid has repeatedly said independence is not up for discussion.
Catalonia pressed ahead with an independence referendum on October 1 that the central government said breached Spain's constitution.
Around 90 per cent of those who cast ballots voted for independence but the poll was poorly monitored and many Catalans opposed to secession boycotted what Madrid branded an illegal plebiscite.
The crisis has caused deep uncertainty for businesses in one of the wealthiest regions in the eurozone's fourth-largest economy.
The stand-off has also put significant strain on the euro but the single currency was up after Puigdemont's announcement and held onto gains in Asian trade today, buying USD 1.1815.
However, it was still down two cents from its recent highs seen last month, with uncertainty continuing to dog the unit.
Stephen Innes, head of Asia-Pacific trading at OANDA, said that while the euro rose it "gained little traction as this is little more than kicking the can down the road. It's unlikely we've heard the last of this debate despite cooler heads prevailing".
But a 2010 move by Spain's Constitutional Court to water down a statute that gave Catalonia additional powers, combined with a deep economic meltdown in Spain, sparked a surge in support for independence.