Catalonia, in northeastern Spain, held its second referendum on independence in three years on October 1.

What happened?

Catalonia voted in favour of independence with 90 percent voting "Yes" in Sunday's referendum, the region's officials have said.

The Catalan government, which said turnout for the referendum was 42 percent, has now opened the door to a unilateral declaration announcing secession from Spain.

"The citizens of Catalonia have won the right to have an independent state in the form of a republic," said Carlos Puigdemont, leader of the Catalan government, on Sunday.

"My government, in the next few days will send the results of today's vote to the Catalan parliament, where the sovereignty of our people lies, so that it can act in accordance with the law of the referendum," he added.

READ MORE: 'Yes' wins Catalonia independence vote marred by chaos

What's next?

It seems clear that Catalonia's leaders now intend to declare independence from Spain in the coming days, triggering a political and constitutional crisis for Spanish Prime Minister Mariano Rajoy's administration.

Such a declaration, though lacking legal force, would present a historic challenge to Rajoy who has accused supporters of independence of trying to "blackmail … the whole nation".

The Spanish constitutional court ordered a suspension of the referendum, following a legal appeal against the vote from Madrid, on September 7.

Spain's 1978 constitution decrees that the country is indivisible, and grants the national government exclusive power to hold referendums.

A Catalonian declaration of independence could force the Spanish government to invoke Article 155 of the constitution, which stipulates that "following approval granted by the overall majority of the Senate" Madrid would be able to suspend Catalonia's current autonomy.

Puigdemont appears unperturbed by such a possibility. Instead, he seems to be politically emboldened following the referendum, which witnessed more than two million people vote "Yes" to independence.

Catalonia has "earned the right to be heard, to be respected and to be recognised", he said on Sunday.

Rajoy, in contrast, faces a fight for his future and the unity of Spain.

He leads a minority government in Madrid whose precarious position may now be exploited by opposition parties seeking to take advantage of this political crisis.

Violence by Spanish police against civilians in Catalonia on Sunday appears to have damaged his position. Ada Colau, the mayor of Barcelona, called for his resignation, accusing him of having "crossed all the red lines with police actions against normal people" that left almost 800 people injured.

Rajoy is due to meet government officials in Madrid on Monday before holding a parliamentary session on the issue.

Pro-independence trade unions in Catalonia have called for a general strike in the region on October 3, according to Reuters news agency.

READ MORE: Catalonia referendum - Who are the Catalans?

Why does it matter?

Catalonia, home to 7.5 million people, accounts for 15 percent of Spain's population and 20 percent of its economic output.

The area's tax revenues form a critical part of Spain's state budget.

Spain is the Eurozone's fourth biggest economy.

As such, the situation presents a major economic concern for Rajoy on top of the mounting political crisis he now faces.