A thousands-strong pro-unity demonstration in Barcelona has seen episodes of tense stand-off between demonstrators and police.

The pro-unity demonstration on Sunday was organized by the Catalan Civil Society group. Around 300,000 people took part in the rally, AFP reported citing municipal police. Organizers claimed over a million protesters opposing independence participated.

Dozens of unionist protesters came to the building of the Catalan parliament in Barcelona. Shouting anti-Catalan slogans, they rattled security barriers, climbed lamp posts, and taunted the police guarding the parliament.

The current march aims to defend Spain’s unity and reject “an unprecedented attack in the history of democracy,” the group behind the event claims, as quoted by AP. The crowds have been marching through the city center heading towards one of the major avenues in Barcelona – the Passeig de Gracia.

Many carried Spanish and EU flags, as well as banners calling for “common sense for co-existence.” Leaders of pro-union parties from the ruling conservatives, pro-business liberals, and socialists are attending the rally, according to AP.

Hoy los catalanes hemos vuelto a salir a las calles de #Barcelona para defender nuestra libertad y la democracia.🇪🇸 #TotsSomCatalunyapic.twitter.com/iV4BkrEd4e — PP Barcelona (@PPBarcelona_) October 29, 2017

Madrid’s official representative in Catalonia, and some members of the central government, have also joined the protest.

The same organization was behind a similar mass rally in Barcelona three weeks ago, when police estimated around 350,000 people took to the streets. Organizers then claimed the figure was over 900,000.

READ MORE: Crowd in Barcelona erupts in cheering as Catalan parliament declares independence (VIDEO)

Earlier this week, Catalonia’s regional parliament declared independence from Madrid following a secret vote. Almost immediately, the Spanish government invoked Constitution Article 155, meaning direct rule over Catalonia, and announced snap elections to be held on December 21.

While Catalan lawmakers were voting on Friday, thousands of people gathered outside the parliament building in Barcelona. The moment the decision to declare independence from Spain was announced, the crowd went wild with excitement, with people dancing and cheering to express their support for the move.