MADRID (AP) — Hundreds of thousands of separatist-minded Catalans have rallied in Barcelona to show their support for an independent nation that would break away from Spain, leaving it without its powerful and prosperous northeastern region.

Barcelona police estimated on their Twitter account that about 540,000 people attended Saturday's demonstration in support of a legally-binding referendum on secession.

Spain argues that an independent Catalonia would be ejected from the European Union and left out from using the euro currency.

Catalan National Day has long been used to mobilize the masses in support of secession from Spain, which has said any referendum on the issue would be unconstitutional. The economically powerful Catalonia accounts for 18 percent of Spain's economic output.