Crowds packed into a bull ring in the port of Tarragona on Thursday night to open the pro-independence campaign for a planned referendum on seceding from Spain.

Supporters sporting makeshift ballot boxes as hats shouted "We will vote!" as they waved around non-official ballot papers.

The Catalan National Assembly, the largest Catalan independence platform, posted images on Twitter of people crowded in the stands and on the floor of the bull ring.

The high-profile event was attended by Catalan President Carles Puigdemont as well as representatives from Catalonia's main pro-independence parties and associations.

The "yes" camp has two weeks to rally support for the vote and win over critics who are reluctant to take part in the referendum, which is due to take place on October 1.

Read more: Catalan independence: Police told to seize ballot boxes

A July poll commissioned by the regional government found that 41.1 percent of Catalans supported independence, while 49.4 percent opposed it. Over 70 percent, however, said they wanted a referendum on the matter.

However, the conservative government of Spanish Prime Minister Mariano Rajoy has argued that the vote would be illegal, and Spain's Constitutional Court has suspended the referendum pending a formal decision by judges.

Backing from Barcelona

The credibility of the referendum got a boost on Thursday when Barcelona's mayor said the vote would be allowed to take place in the city.

Mayor Ada Colau tweeted that people would be allowed to vote "without putting institutions or public workers at risk." She said the regional government's facilities in Barcelona will be used as polling stations.

Colau initially refused to make local public facilities available out of concern that civil servants could lose their jobs. She also warned that facilitating the vote could be considered illegal.

Read more: Pro-independence Catalans celebrate Diada national day ahead of vote

No financial accounts to Madrid

Catalonia's regional government also said in a letter that it would no longer send weekly financial accounts to Madrid.

In July, the Spanish government ordered the region to send its weekly accounts to prove Catalonia was not using public money to promote the referendum.

In a letter to Spanish Budget Minister Cristobal Montoro, Catalan Deputy Governor Oriol Junqueras said the arrangement implied "political control that is not related to the objectives of budget stability or to the purposes of state legislation in this matter."

Criminal probe against pro-referendum mayors

On Wednesday, Spain's state prosecutor launched a criminal probe into some 712 Catalan mayors who have backed the vote. They also instructed police to arrest the mayors should they fail to respond to the summons.

Catalonia, which is roughly the size of Belgium, accounts for one-fifth of Spain's economic output. The region already has significant powers over matters including education and health care.

rs/cmk (AP, AFP, Reuters)