Thousands of fans held up blue banners with the words 'Spain, sit and talk' as Barcelona and Real Madrid kicked off the first Clasico of the season at the Camp Nou on Wednesday.
The banners were given to supporters outside the ground and carried the words, 'Freedom, rights, self-determination', as well as the slogan of Democratic Tsunami, the protest group promoting the cause of Catalan independence.
Protestors had also blocked traffic after gathering at the four corners of the stadium from 1500 GMT, four hours before kick-off.
Lionel Messi and his Barca team-mates arrived in their team bus just before 1800 GMT while bitter rivals Real pulled through the gates around five minutes later, after the two sides had travelled from the same hotel.
Real's bus had been accompanied by whistles and insults from fans on its short trip to the Camp Nou, where they were playing Barca for top spot in La Liga.
As he entered the stadium, Real's club president Florentino Perez gave a thumbs up when asked about the journey in.
"We must take advantage of the magnitude of this match so the world can see our situation from Europe and around the world," said Antoni Rabull, a 73-year-old retiree.
There was a visible police presence outside the stadium but little sign of trouble as protestors stayed true to Democratic Tsunami's pledge to carry out its demonstrations peacefully.
"To perform the action of Democratic Tsunami it is essential that the game can be played and the fans with tickets can enter the stadium," the group wrote on Twitter.
Police were also stationed outside the nearby Hotel Princesa Sofia, where players, coaching staff and referees were instructed to convene, before leaving together for the match two hours before kick-off.
Around 3,000 security personnel were posted around the stadium after renewed fears of unrest. The original fixture in October had to be postponed due to violent demonstrations breaking out across Catalonia.
- 'Spain, sit and talk' -
Barcelona newspaper La Vanguardia claimed there were plans to throw inflatable balls onto the pitch to denounce the use of rubber bullets by police during the October riots.
"Tsunamis are like water, they adapt to and adopt ideas," read a message posted on Twitter by Democratic Tsunami on Wednesday morning.
"We accept the #ChallengeLaVanguardia and call on everyone to throw an inflatable ball and write a message to the world."
Other posts from the same account added: "At 8pm, everyone will be able to see the match and the message 'Spain, sit and talk' will be transmitted around the world.
"The actions of today, like all of Democratic Tsunami's, will be strictly non-violent."
Barcelona had issued a statement on Tuesday night to fans planning to attend the game, advising supporters to use public transport, allow plenty of time and warning of "exhaustive security checks" at entrances to the stadium.
Barca also called for calm around the fixture, asking fans "to come to the game at Camp Nou on Wednesday to support the team".
- Catalan uprising -
Protests broke out in October after nine separatist leaders were sentenced to heavy prison sentences for their involvement in the independence referendum of 2017.
As well as the massive security presence in Barcelona, the numbers of private security staff in the stands were also be increased to reduce the threat of pitch invasions that could interrupt the game.
"The operation will ensure that the Clasico is played normally," said the chief commissioner of the Catalan regional police Eugeni Sallent.
Democratic Tsunami hopes to transmit its message through the world's most watched club football fixture, which has an estimated global audience of 650 million.
Barcelona have historically had a close association with Catalan nationalism, with Camp Nou routinely used as a setting for flags, banners and chants in support of the cause.
The club could suffer the consequences of any altercations or interruptions during the game.
At a meeting in Madrid last week, the RFEF warned it "will apply the regulations in force," which range from heavy economic sanctions to the closure of Camp Nou to supporters.
Demonstrators hold Catalan pro-independence "Estelada" flags during a protest called by Catalan separatist movement Democratic Tsunami outside the Camp Nou
A banner reading "Change the state of things" by the Catalan separatist movement Democratic Tsunami hangs from a building next to Barcelona's Camp Nou stadium prior to Wednesday's hotly-anticipated Clasico
Barcelona supporters wave Catalan pro-independence "Estelada" flags before the Clasico