Nearly 1.5 million Catalans took to the streets of Barcelona on Friday to rally for independence, as the region’s politicians launched their campaigns for a looming election billed as a make-or-break moment for Catalonia.

“This is the most important campaign of our lives,” said Raul Romeva of the pro-independence Junts pel Sí (Together for Yes) party. A coalition made up of the Catalan leader Artur Mas’s conservative CDC party and the leftwing Catalan Republic Left, Junts pel Sí is seeking to turn the 27 September regional ballot into a quasi-referendum on independence. “We are asking the people what they want to be and where they want to go,” said Romeva.

Facebook Twitter Pinterest People wave Estelada flags, representing Catalan independence, in Meridiana Avenue. Photograph: Jordi Boixareu/Zuma Press/Corbis

The formal campaign began on Catalan National Day, a holiday that in recent years has become a show of strength for secession-minded Catalans with massive rallies staged in support of breaking away from Spain. This year, in a nod to the politically charged backdrop, organisers of the rally adopted the slogan “Let’s start building a new country.”

Last year more than 1 million Catalans turned up to demand a referendum on independence. After several attempts to hold such a vote proved unsuccessful, Mas called early elections in the 7.5-million-strong region earlier this year.

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“We tried to do everything before getting to this point,” said Mas on Friday, as he described years of rising political tensions between Catalonia and Madrid. “Absolutely everything.”

If Junts pel Sí wins a majority of seats in the 135-seat parliament, Mas has pledged to lead a transitional government that will begin drafting a Catalan constitution and attempt to negotiate secession with the central government. A majority would also give Mas a mandate to unilaterally declare independence by 2017.

Most polls show that pro-independence parties are poised to win a slim majority. This week, the state-sponsored Centre for Sociological Research released a poll suggesting Junts pel Sí is on track to win 38.1% of the vote (60 to 61 seats). If they join forces with the pro-independence, far-left party CUP, projected to win eight seats, the separatists could eke out the majority they need to begin the process of breaking away from Spain.

Facebook Twitter Pinterest Hundreds of thousands of Catalans fill the streets demanding independence, before a regional election billed as an indirect vote on breaking away from Spain. Photograph: Lluis Gene/AFP/Getty Images

On Friday, Mas made it clear that the use of elections to take the pulse of an independence movement was far from ideal. But he argued that the result would have to be accepted as legitimate by the international community, as it was the only option available to the region’s leaders. “If you can’t hold a real and specific referendum, if all your attempts have been blocked, you have to do something,” said Mas. “This is the only tool I have in my hands.”

He said the preference for those leading the independence movement remains a referendum like that held in Scotland last year. “Imagine if in Scotland there hadn’t been a referendum. Would the alternative have been to do nothing?”

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Spain’s prime minister, Mariano Rajoy, and his conservative People’s party have shut down all attempts to hold a formal referendum in Catalonia, arguing that the country’s constitution prevents regions from unilaterally making decisions that affect all Spaniards.

As the elections in Catalonia drew nearer, Rajoy reiterated that any move towards independence in Catalonia would be blocked. “No Spanish prime minister would accept this – neither myself or any other – unless he goes crazy,” he said in a recent radio interview.

In recent days, Rajoy’s hardline stance has been backed by David Cameron and Angela Merkel, with the British prime minister warning that an independent Catalonia would be left out of the EU.

Across Barcelona, many of those who turned out to take part in the rally for independence referred to central government to explain their own stance.

Facebook Twitter Pinterest Demonstrators unfold a big Estelada flag during celebrations on Catalan National Day. Photograph: Lluis Gene/AFP/Getty Images

“They keep saying no to everything we want,” said Teresa Mestres, 71. “And every time they say no, more of us become pro-independence.” Mestres recalled her childhood during the Franco dictatorship, when speaking Catalan in schools was banned, and worried that rising tensions between Madrid and Barcelona could erase the cultural freedoms gained since the death of Franco. “Every day they prohibit more and more,” she said. “We want to make sure the next generations can enjoy the things that we couldn’t.”

For others, the day was a chance to celebrate that the once distant possibility of independence might now be within reach. Joan Carlos Nonell, 60, said he had dreamed of an independent Catalan state since he was seven years old. “Now it feels like it could be a possibility: people are starting to see that we can’t continue like this,” he said.

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While polls suggest the majority of Catalans support the idea of a referendum, polls also show the region is deeply divided on the issue of independence. Alongside those ardently committed to independence, Friday’s rally attracted many who simply want more self-governance for the region in the belief that it would allow Catalonia to be able to better address issues such as unemployment and corruption.

“It’s not that I want to separate,” said Carles Rossell, who had travelled to Barcelona from nearby Maresme with his two daughters, dressed in yellow and draped in Estelada flags. “It’s that we want things to get better, we need things to get better,” he said, echoing many in the region who argue that Catalonia pays more in taxes to central government than it receives in services and infrastructure.

Sitting on a park bench, Palmira Serrano, 56, said she was tired of the political stalemate that had played out between Catalonia and Madrid in recent years. “We just want Spain to listen to us,” said “For years they’ve been turning their back on us.”

Referring to the small graphics design company she owned with her husband, Serrano said: “We pay taxes that go to Madrid and never come back to us. So you get to a point where you say: ‘Maybe it’s time to leave.’”