Spanish officials are seeking charges of rebellion, sedition and embezzlement for members of the ousted Catalan cabinet and the governing body of the regional parliament that allowed a vote to declare independence last week.
The crimes can be punished with up to 30, 15 and six years in prison respectively.
Spain's chief prosecutor Jose Manuel Maza said he would ask judges for preventive measures against the officials, but did not specify if those would include immediate arrest and jailing while they await trial.
He said one lawsuit seeks charges for ousted Catalan officials in the country's National Court. That includes regional leader Carles Puigdemont and his number two, Oriol Junqueras, although Mr Maza did not name them.
He said a second lawsuit concerning members of the governing body of Catalonia's parliament, including speaker Carme Forcadell, was filed in the country's Supreme Court.
Some elected officials in Spain, including regional legislators, enjoy a degree of immunity before courts and can only be tried in the highest court.
Mr Maza spelled out the charges in a brief appearance before cameras in Madrid.
It came as Catalonia's civil servants returned to work for the first time since Madrid rejected the independence declaration by imposing direct control.
Dismissed Catalan president Mr Puigdemont meanwhile had left Spain for Belgium. An anonymous Spanish government official said Mr Puigdemont had travelled to Brussels.
Belgian asylum state secretary Theo Francken has said it would be "not unrealistic" for Mr Puigdemont to request asylum.
As staff arrived at the headquarters of the Catalan government in Barcelona, Mr Puigdemont posted a photo on Instagram of a courtyard at the seat of the regional presidency building. Both the Catalan and Spanish national flags waved from the top of the building.
The ambiguous Instagram post, accompanied by the words "Good morning" in Catalan and a smiley emoticon, left many guessing whether he was inside the building. There was no indication of when the photo was taken.
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As dozens of journalists, curious onlookers and bemused tourists gathered in the square outside the Gothic government palace in central Barcelona, at least one portrait of Mr Puigdemont was still hanging on a wall inside the Generalitat building.
At least one member of the ousted government defied his dismissal by showing up at work and posting a photo on Twitter from his formal office.
"In the office, exercising the responsibilities entrusted to us by the people of Catalonia," said Josep Rull, who until last week was the region's senior official in charge of territorial affairs.
Two police officers entered and left the building, followed minutes later by Mr Rull, who told reporters and supporters that he would continue carrying out his agenda.
Spanish authorities say deposed officials will be allowed to take their personal belongings from official buildings, but are barred from performing any official duties.
