TARRAGONA, SPAIN –

Protesters calling for Catalan independence kicked off Spain's bi-annual human towers building competition on Sunday that is being held for the first time since Catalonia's failed 2017 independence referendum.

Though the competition is not an official pro-independence event, human towers building is a deep-rooted tradition of the Catalan culture where participants are considered either supporters of or in favor of secession from Spain.

The event, which drew 6,000 spectators in the northeastern city of Tarragona, comes almost a week after tensions flared up again with thousands marching in Barcelona to mark the anniversary of the Oct. 1 2017 referendum.

Opinion polls in Catalonia show a relatively even split between those who favour remaining in Spain and those wanting to secede.

People carried a huge Esteleda, the Catalan separatist flag, inside the Tarraco Arena Placa in Tarragona when the finals for the competition started with the official national anthem of Catalonia "Els Segadors" ("The Reapers").

Some shouted pro-Catalan independence slogans while others displayed banners demanding the release of imprisoned pro-secessionist politicians and the return of those in exile.

After the five minute protest, the spectators turned their attention to the event which brought 42 teams of "castellers" competing to build the most complex human tower.

Catalan leader Quim Torra, who last month relaunched a campaign for his region to split from Spain, attended the finals of Human Tower Competition which was declared a Cultural and Intangible Heritage of Humanity by UNESCO in 2010.

The competition is a three-day event with the first part held in the Catalan city of Torredembarra on Sept. 30, followed by this weekend's festivities in Tarragona.

The winners are awarded €16,000 ($18,400) in prize money, according to the Tarragona City Hall, the organizer of the event.