"By proving itself incapable of finding a solution during all this time, the Spanish government has allowed the Catalan conflict to escalate from an internal dispute to a European conflict", Colau said.
Tackling one of the biggest political crises to hit Spain since democracy was restored in the 1970s after decades of dictatorship, authorities in Madrid have declared the referendum unconstitutional and told police to ensure no votes are cast. People will demonstrate and show what they think about this situation.
Nearly 10 million ballots were seized last week, although the whole population of Catalonia is a little more than 7.5 million, including those who are not eligible to vote.
Kathleen Brooks, the research director at City Index, said a referendum win for the separatists could cause the euro to decline by as much as 5%.
The Mossos have said the order to close voting stations increased the risk of confrontation between demonstrators and police, a worry shared on Thursday by two United Nations experts.
If arrests and negotiation don't stop the movement, Spain's central government has the option of using Article 155 of the constitution and officially suspending self-government in Catalonia.
National and regional security forces have been ordered to prevent any activity connected to setting up polling stations, seal off buildings, and confiscate computers and all material related to the ballot.
Spain's economy minister told the FT that a Catalan exit would also mean an automatic exit from the European Union and eurozone, subjecting 75% of the region's production to export tariffs - but not everyone agrees.
And Catalonia's separatist executive has vowed to go ahead despite Madrid's ban. "It is basically [about] how the Catalonians decide its future".
Catalan authorities say they will declare independence within 48 hours after announcing the vote's results if the "yes" side wins.
He said the "silent majority" of Catalans who oppose the referendum would not protest in the streets to avoid raising tensions.
Meanwhile, media freedom watchdog Reporters Without Borders complained that journalists were the target of pressure from both the pro and anti-independence camps.
Spain's cabinet spokesman said Friday there will no referendum on Sunday and warned Catalan officials that they would "face consequences" for pressing ahead with a vote that was suspended by the country's Constitutional Court.
"I prefer to remain with what is known than with what will come because it could be very good or very bad", she told AFP.