Spanish Prime Minister Mariano Rajoy has taken the first step towards activating article 155 of the Spanish constitution.
Article 155 is a so-called nuclear option that would allow Mr Rajoy to suspend Catalonia's political autonomy and take over the region.
"The cabinet has agreed to formally ask the Catalan government to confirm whether it has declared independence," Mr Rajoy said in a televised address.
"The answer from the Catalan president will determine future events, in the next few days," he also said, adding he would keep acting in a "cautious and responsible" way.
This formal requirement is needed to trigger the article 155, though the constitution does not establish any specific time frame for the answer.
A spokesman for the regional government in Catalonia has said a declaration of independence signed by Catalan leader Carles Puigdemont and fellow separatist politicians is merely a "symbolic act."
Catalan government spokesman Jordi Turull said the declaration yesterday evening was "a symbolic act in which we all signed our commitment to declare independence," but added that the official declaration "must be made by the Catalan parliament".
The Spanish government is preparing to hold crisis talks after the "suspended" declaration of independence, as Catalan leaders called for negotiations.
Mr Rajoy chaired an emergency cabinet meeting in response to the announcement by Mr Puigdemont that he had accepted "the mandate of the people for Catalonia to become an independent republic" following a banned referendum earlier this month.
The Spanish leader 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.
At stake is the future of a region of 7.5 million people, one of Spain's economic powerhouses, whose drive to break away has raised concern for stability in the European Union.
Crowds of thousands gathered outside the parliament building in Barcelona yesterday 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.
But Spain's political establishment rounded on Mr Puigdemont following the declaration, while support among separatists in Catalonia was mixed.
Deputy prime minister Soraya Saenz de Santamaria told reporters shortly after the signing that Mr Puigdemont was "a person who doesn't know where he is, where he's going or with whom he wants to go".
Political leaders in Catalonia, Spain, and Europe have come out against secession, concerned over the country's biggest upheaval since its transition to democracy in the 1970s.
Spain and Catalonia now enter into the unknown, as the government has repeatedly said independence is not up for discussion.
Catalonia pressed ahead with an independence referendum on 1 October that the central government said breached Spain's constitution.
Around 90% of those who cast ballots voted for independence but turnout was only 43%, the poll was poorly monitored, and many Catalans opposed to secession boycotted what the government 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.
Demands for independence in Catalonia, which has its own language and cultural traditions, date back centuries.
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.