Thousands of flag-waving supporters of Spanish unity made their presence felt on Saturday outside Madrid's city hall, a day before the Catalan independence referendum.

"Madrid supports all those Catalans who don't want to break up the country and who believe that we are stronger together," the filmer wrote online.

Tens of thousands of Catalans are expected to vote in the ballot, which will have no legal status as it has been blocked by Spain’s constitutional court.

Madrid has sent thousands of police to the region to stop it taking place.