(reuters) -- The referendum, declared illegal by Spain’s central government, has thrown the country into its worst constitutional crisis in decades and raised fears of street violence as a test of will between Madrid and Barcelona plays out.

In a sign of how the planned vote has polarized the country, thousands of pro-unity demonstrators gathered in Spain’s major cities, including Barcelona, to express their fierce opposition to Catalonia’s attempt to break away.

In the region itself, hundreds of supporters of the referendum spent the day with their children playing football, board games and ping pong in schools, traditionally used as voting stations in Spain, to keep them open until voting starts at 9 a.m. (0700 GMT) on Sunday.

The government said just a small percentage of schools were occupied, however, and that it had verified that most of the more than 2,300 earmarked for the vote were closed.

In those where they gathered, parents brought sleeping bags and prepared to bed down on gym mats.

“We don’t understand why we can’t express in a peaceful manner the simplest expression of democracy - a vote,” said Pablo Larranaga, as he stood in a school in Barcelona surrounded by parents and small children.

(Photo: Anti-independence protesters carry a huge Spanish flag through the streets of Barcelona ahead of Catalonia's referendum on Sunday CREDIT: ANADOLU AGENCY)