The Spanish government has stripped Catalonia's most senior police officials of their powers, hours after direct rule was imposed on the region, according to media reports.
This is the first specific measure taken since the Catalan parliament voted to declare independence.
Prime Minister Mariano Rajoy has also announced the dissolution of the regional parliament and the removal of the Catalan leader, and called snap local elections.
Demonstrations for and against independence went on into the night.
More are expected on Saturday (Oct 28), with a rally "for the unity of Spain and the constitution" to be held in Madrid.
The crisis began when Catalan leaders held an independence referendum, defying a ruling by the Constitutional Court which had declared it illegal.
The Catalan government said that of the 43% of potential voters who took part, 90% were in favour of independence. Others boycotted the vote after the court ruling.
The Madrid government sacked Catalonia's president and dismissed its parliament on Friday (Oct 27), hours after the region declared itself an independent nation in Spain's gravest political crisis.
A new regional election will be held in Catalonia on Dec 21, PM Mariano Rajoy said in a televised address on a day of high drama.