Barcelona was a sea of red and yellow as crowds carrying separatist flags marched in the city to celebrate Catalan National Day. Organisers hoped to attract at least 500,000 people for a pro-independence rally using the slogan "Let's start building a new country".

Catalonia National Day
People pose in front of a giant Catalan flag at the Arc de Triomf in BarcelonaDavid Ramos/Getty Images
Catalonia National Day
David Ramos/Getty Images
Catalonia National Day
David Ramos/Getty Images
Catalonia National Day
Thousands of people march during a Catalan pro-independence demonstration in BarcelonaDavid Ramos/Getty Images
Catalonia National Day
Demonstrators unfold a big pro independence flag during celebrations of Catalonia's National DayGerard Julien/AFP

Separatist parties chose Catalonia's national day – or "Diada" – to launch their campaign to elect a majority of secessionists in regional parliamentary elections due to be held on 27 September. Pro-independence parties need 68 seats in the 135-member parliament to push forward. Polls show them on track to win a slim majority.

Independence backers say a win would give them a mandate to start drafting a Catalan constitution and attempt secession negotiations with the central government. A unilateral declaration of independence could be made by the parliament by 2017. A failure to achieve a majority would deal a serious blow to the movement, which has been losing steam since a symbolic referendum on independence last year.

Catalonia National Day
The Catalan flag is projected on the facade of the Palau de La Generalitat, the Catalan government headquarters, in BarcelonaLluis Gene/AFP
Catalonia National Day
Demonstrators wave a huge Catalan flag as they march in Vilafranca del PenedesDavid Ramos/Getty Images
Catalonia National Day
Demonstrators holding torches march during a Catalan pro-independence demonstration in Vilafranca del PenedesDavid Ramos/Getty Images
Catalonia National Day
David Ramos/Getty Images
Catalonia National Day
David Ramos/Getty Images
Catalonia National Day
David Ramos/Getty Images
Catalonia National Day
David Ramos/Getty Images
Catalonia National Day
Regional flags are seen on the clothing of someone taking part in a pro-independence rally in BarcelonaDavid Ramos/Getty Images
Catalonia National Day
Artur Mas, president of the Catalonia regional government, takes part in a ceremony at the Rafel de Casanovas monument in BarcelonaJosep Lago/AFP
Catalonia National Day
Artur Mas, Oriol Junqueras, Raul Romeva, Carme Forcadell and Muriel Casals put their hands together during a rally for Junts pel Si, a coalition of pro-independence parties, in BarcelonaGustau Nacarino/Reuters

Polls show that Catalans overwhelmingly support the right for a referendum, but are evenly divided over whether they actually want the region to be independent.